Tethyan Zinc-Lead Metallogeny in Europe, North Africa, and Asia
Published:January 01, 2010
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Neal A. Reynolds, Duncan Large, 2010. "Tethyan Zinc-Lead Metallogeny in Europe, North Africa, and Asia", The Challenge of Finding New Mineral Resources: Global Metallogeny, Innovative Exploration, and New Discoveries, Richard J. Goldfarb, Erin E. Marsh, Thomas Monecke
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The Tethyan belt extends throughout the circum-Mediterranean and eastward through Turkey, Iran, and Pakistan to China and Southeast Asia. The belt is characterized by rift zones with bimodal volcanic rocks and thick clastic sedimentary rock fill, passive-margin basins with platform carbonates, and calc-alkaline island-arc volcanic rock sequences. It is known primarily for its copper and gold endowment, but it includes several large and globally significant zinc-lead provinces. These include the Basque-Cantabrian basin (Réocin) in northern Spain, the Atlas zinc-lead district in Morocco, Algeria, and Tunisia, the zinc-lead-silver deposits in the Balkans—including the Trepča district extending south to Macedonia and Greece—the zinc districts in central Anatolia, Turkey, and Iran—such as Angouran and Mehdiabad—and deposits such as Padaeng, in Thailand, and Jinding, in southwestern China.
Late Carboniferous to Triassic rifting in northern Gondwana and opening of the Neotethys Ocean marks the commencement of the most significant zinc-lead metallogenic cycle and initiated the break-up of Pangea. Rifting migrated eastward and broad Permian to Cenozoic carbonate shelf and passive-margin basin sequences were deposited. The thick carbonate sequences provided ideal trap settings for MVT deposits, with zinc- and lead-rich mineralizing fluid flow initiated by Cretaceous to Cenozoic inversion, collision, and uplift on the Tethyan margins. High-temperature carbonate-replacement and vein-type mineralization is also associated with magmatically induced hydrothermal activity during the Cenozoic compressional events. Unusual hybrid deposits involved both basinal and magmatic fluid inputs. Subsequent uplift and oxidation has resulted in the development of economically significant nonsulfide zinc deposits throughout the belt.
The Tethyan Belt encompasses the circum-Mediterranean and much of central Europe and south-central Asia from Turkey to Pakistan, extending through Tibet and including the southern half of China and Southeast Asia. The belt represents a succession of Tethyan oceans developed through rifting on the northern margin of Gondwana and closed through northward drift and collision of rifted terranes with Laurussia and Eurasia over a prolonged period from the early Paleozoic to the Cenozoic (Metcalfe, 1999; Stampfli, 2000; Stampfli and Borel, 2002; Stampfli and Kosur, 2006). Each cycle shows an evolution from rift-sag sedimentary basins to passive-margin basins, commonly with extensive platform carbonates, to convergent and collisional margins with calcalkaline volcanism. The cyclic development of the Tethyan oceans was punctuated by the amalgamation and break-up of Pangea in the Carboniferous to the Permian.
For the purposes of this discussion, the focus will be on mineralization formed in the evolving late Paleozoic to Cenozoic Neotethys cycle, which commenced with the rifting of the Cimmerian terranes from Gondwana and Pangea during the formation and collapse of the Variscan orogen in Eurasia (Metcalfe, 1999; Stampfli and Borel, 2002; Stampfli and Kosur, 2006). The older Paleozoic Paleotethys tectonic cycles are not considered.
Although the Tethyan metallogenic belt is best known for its porphyry and epithermal copper and gold deposits (Lips, 2007), this paper will emphasize the zinc-lead endowment of the belt. The Tethyan belt hosts a range of globally significant zinc-lead deposits and districts, including Jinding in China, Angouran in Iran, Silesia in Poland, and Réocin in Spain (Fig. 1; Table 1).
Whereas the details of the evolution of the Tethyan belt have been described by a number of workers (e.g., Şengör, 1984; Metcalfe, 1988, 1996a, b, 1999—updated on website http://www-personal.une.edu.au/˜imetcal2/Palaeogeog.html; Stampfli, 2000; Stampfli and Borel, 2002—updated on website http://www.unil.ch/igp/page76652.html), this discussion will focus on the relationship of various types of zinc-lead deposits to the evolution of particular domains within the Tethyan tectonic collage. The tectonic settings of significant districts are described in order to illustrate their control on styles of zinc-lead mineralization, as well as to understand the relationships between districts and to assess additional discovery potential.
Significant factors influencing zinc-lead metallogeny in the belt include:
Deposition of extensive and thick carbonate shelf sequences on the passive margins of migrating cratonic domains, dominating much of the Mesozoic and Cenozoic successions. This provided ideal host rocks for Mississippi Valley type (MVT) and other styles of carbonate-hosted zinc-lead mineralization.
Development of rift-sag basinal sequences at various stages of Tethyan evolution in favorable settings for the formation and preservation of sediment-hosted massive sulfide (SHMS) or Sedex deposits.
Emplacement of intrusive and volcanic complexes in convergent and postcollisional arc settings, favorable for formation of high-temperature zinc-lead carbonate-replacement deposits (CRD or manto) and skarn deposits due to the prevalence of calcareous sequences.
Subsequent uplift and oxidation resulting in the development of economically significant nonsulfide (“oxide”) zinc deposits throughout the belt.
Tectonic Framework for Zinc-Lead Metallogeny
Zinc-lead metallogeny in the Tethyan belt can be broadly subdivided into “basinal” and “magmatic” settings. Basinal settings related to evolution of sedimentary basins encompass SHMS and MVT styles. Magmatic settings encompass volcanic-hosted massive sulfide (VHMS) and intrusion-related (skarn, CRD/manto and epithermal) deposits.
The different zinc-lead deposit types can be broadly related to different stages of the tectonic cycle. The SHMS deposits typically form during extension in rift-sag basins (Goodfellow and Lydon, 2007), although some deposits have been related to inversion phases (e.g., Century: Broadbent et al., 1998). The MVT deposits encompass a range of epigenetic low-temperature carbonate-hosted deposit styles commonly hosted within meteoric or hydrothermal karst systems (Leach and Sangster, 1993). Most MVT districts formed within orogens or in orogenic forelands from large-scale fluid-flow systems driven by compression and uplift (Bradley and Leach, 2003). Leach et al. (2001) related cycles of MVT development in geologic time to periods of terrane amalgamation and super-continent formation. However some MVT deposits formed earlier in basinal history from fluid-flow systems driven by major extensional rifting or inversion events (e.g., Lennard Shelf, Dörling et al., 1998; Alpine deposits, Leach et al., 2003). Irish-type deposits, particularly the type examples in the Irish midlands, have been the subject of debate regarding timing of mineralization and affinity with either SHMS or MVT deposit types (e.g., Samson and Russell, 1987; Hitzman, 1995; Wilkinson, 2003; Leach et al., 2005).
VHMS deposits can form in a variety of submarine volcanic settings, but Phanerozoic zinc-rich deposits typically form during extensional phases along convergent plate margins, and some systems may be transitional with SHMS in rift or back-arc settings (Franklin et al., 2005; Huston et al., 2010). Intrusive-related deposits, including CRD, skarn, and epithermal types, are typically associated with calc-alkaline magmatic arcs on convergent plate margins, preceding or accompanying collisional events. Although skarn and CRD zinc-lead deposits may be associated with porphyry copper deposits (e.g., Bingham district, Babcock et al., 1995; Meinert et al., 2005), some large CRD districts and deposits have no spatial association with porphyry copper belts (Megaw et al., 1988).
Economically important deposits of all of the above styles occur in the Tethyan belt (Fig. 2) and can be related to evolution of the Tethyan tectonic cycle. MVT systems formed during Cenozoic compression and collision are the most widely developed. Few large VHMS deposits are known, and SHMS deposits are also not well represented. Significant intrusive-related deposits occur within arc belts, such as those that formed during postcollisional extension in the Balkans. Some carbonate- and volcanic rock-hosted systems are hybrid, with evidence for a basinal brine origin but with significant magmatic influence on hydrothermal systems as fluid source or heat engines. Nonsulfide zinc deposits formed by supergene modification of hypogene deposits provide a small but significant contribution to the zinc endowment.
Tethyan tectonic overview
Most recent plate tectonic reconstructions propose similar key elements of Tethyan evolution (e.g., Şengör, 1984; Ziegler, 1988; Metcalfe, 1999, 2002; Stampfli and Borel, 2002; von Raumer et al., 2003). Tethys is considered as the ocean that developed on the northern margin of Gondwana in the early Paleozoic, persisted on the eastern side of Pangea in the late Paleozoic, extended westward by rifting break-up of Pangea in the Mesozoic, and was finally closed in the Cenozoic (Fig. 3). This history encompasses two main phases. Paleotethys originated with Gondwana break-up in the early Paleozoic and concluded with collision of the Cimmerian terranes with Asia in the early Mesozoic. Neotethys developed between the Cimmerian terranes and Gondwana in the latest Paleozoic, extending westward through rifting of Pangea in the Mesozoic, and culminated with collision of Africa, Arabia, and India, with Europe and Asia in the Cenozoic.
Neotethyan extension, rifting, and spreading
The terranes that separated from Gondwana and drifted northward in the Permo-Triassic, thus forming the Neotethys Ocean are collectively referred to as Cimmeria and are present in the Balkans, much of Turkey through central Iran, and central Tibet to western Southeast Asia, where the term Sibumasu has also been applied to these blocks (Şengör, 1984; Şengör et al.. 1984; Metcalfe, 1999, Stampfli and Borel, 2002). In eastern Gondwana, Neotethyan extension preceding rifting commenced in the Late Devonian, culminating in separation of Sibumasu (eastern Myanmar, western Thailand, western Malaysia and Sumatra) and Qiangtang (central Tibet) in the latest Carboniferous (Metcalfe, 1999, 2002). Late Carboniferous extension in eastern Gondwana coincided with the Hercynian-Alleghanian orogeny in western Gondwana and collision with Laurussia (Laurentia-Baltica-Siberia) to form Pangea, reflecting anticlockwise rotation of Laurussia relative to Gondwana (Stampfli and Borel, 2002; Stampfli and Kosur, 2006—updated on website http://www.unil.ch/igp/page76652.html).
The western Cimmerian terranes of central Iran (Sanandaj-Sirjan), Turkey (Taurus), and southeastern Europe (Serbo-Macedonian Massif) separated from Gondwana by the Late Permian, with rifting migrating diachronously westward and propagating through the Atlas belt to the incipient North Atlantic in the Triassic (Stampfli and Borel, 2002—updated on website http://www.unil.ch/igp/page76652.html).
There is a marked absence of zinc deposits within rift-sag basins directly associated with Neotethyan extension and rifting; the Carboniferous Sopokomil SMHS deposit in Sumatra is the most significant known example. Early Carboniferous MVT zinc-lead deposits in northwestern Australia (Lennard Shelf and Bonaparte basin) may be related to earlier extension in northern Gondwana.
Opening of the Neotethys Ocean, with commensurate Paleotethys Ocean closure, was defined by rapid northward drift of the Cimmerian terranes driven by subduction along the northern Paleotethys margin from Turkey, through central Asia, to southern China and Indochina (Metcalfe, 1996b; Stampfli and Borel, 2002). Convergence culminated in diachronous westward collision from Late Triassic to Jurassic and final closure of Paleotethys, a fundamental event in the assembly of the Eurasian continental collage, generally referred to as the Indosinian orogeny in eastern Asia and the Cimmerian orogeny in central and western Asia and Europe (Şengör, 1984; Şengör et al., 1984; Stampfli and Kosur, 2006).
Neotethyan subduction and closure
Following the Indosinian-Cimmerian orogeny, subduction commenced along the northern margin of the Neotethys Ocean in the Early Jurassic (Stampfli and Borel, 2002). An array of Jurassic-Cretaceous back-arc oceanic basins formed from central Europe to central Asia, in part as successor basins to Paleotethys (Stampfli and Borel, 2002, Stampfli and Kosur, 2006—updated on website http://www.unil.ch/igp/page76652.html). Zinc-lead metallogeny related to convergent and collisional tectonism on the northern Tethyan margin includes VHMS deposits in the Pontide belt of Turkey and skarn-manto deposits (or CRD) in the Balkans.
In the Late Jurassic-Early Cretaceous, final Gondwana break-up on the southern Neotethys margin resulted in the separation of Africa, India, and Antarctica-Australia and the initial opening of the Indian Ocean (Stampfli and Borel, 2002). The best examples of zinc-lead mineralization associated with Gondwana break-up on the southern Tethys margin are the Jurassic Duddar SHMS deposit in Pakistan and the Jabali MVT deposit in Yemen.
Initiation of rapid South Atlantic opening from late Early to Late Cretaceous resulted in anticlockwise rotation of Africa relative to Laurasia, cessation of Neotethys spreading and convergence between Eurasia and Africa and/or Arabia (Stampfli and Borel, 2002; Stampfli and Kosur, 2006). These events marked the commencement of Neotethys closure (Fig. 3). The succession of collisional events on the northern Tethyan margin began with docking of the Lhasa terrane in the Late Cretaceous, coincident with arc-continent collision along the southeastern Asian margin from West Burma to Woyla in Sumatra (Metcalfe, 1999). Indian collision commenced in the Eocene with maximum uplift in the Miocene. In the west, subduction within the Pyrennean-Alpine-Carpathian-Pontide belt resulted in closure of back-arc basins by the Eocene and associated orogenic uplift. Subsequent initiation and roll-back of northward subduction of oceanic crust in the western Mediterranean resulted in arc collision with the North African passive margin during Atlas orogenesis in the middle Miocene (Rosenbaum et al., 2003). Collision of Arabia with Eurasia along the Zagros fold belt commenced in the Oligocene, resulting in Miocene uplift and westward displacement of Anatolia, with far-field uplift in the Caucasus belt.
The long and complex Cretaceous to Cenozoic Alpine-Himalayan orogeny is the most significant for Tethyan zinc-lead metallogeny and resulted in the formation of major MVT deposits in southern and central Europe, north Africa, south-western to central Asia, southwestern China and Southeast Asia, as well as important intrusion-related CRD, skarn, and epithermal zinc-lead-silver deposits.
Paleogeography and climate
Based on recent plate tectonic reconstructions (e.g., Ziegler, 1988; Stampfli and Borel, 2002), Neotethys occupied tropical latitudes through much of its history and is associated with extensive carbonate deposition from the Permian to the Cenozoic. Carbonate deposition was also favored by the prevalence of broad continental shelves on passive cratonic margins, from Carboniferous to Triassic on the northern Neotethys margin, and from Carboniferous to Miocene on the southern margin. Evaporites were also widely deposited, especially in the rift-stage tectonic settings.
In the Cenozoic, much of the Tethyan belt was located in tropical to arid subtropical climate zones. This has facilitated widespread oxidation of sulfide deposits, particularly in up-lifted collisional mountain belts (Hitzman et al., 2003).
Sediment-Hosted Massive Sulfide Zinc-Lead Mineralization Related to Neotethyan Rifting
Neotethyan rifting commenced in the Late Devonian in eastern Gondwana (Metcalfe, 1999) and ceased in the Jurassic in western Gondwana as the Atlas rifts evolved to sagphase deposition (Fig. 3). The SHMS zinc-lead deposits that can be directly related to rift-sag basin evolution through this belt are limited. Two deposits can be highlighted, the Carboniferous Sopokomil deposit in Sumatra and the Jurassic Duddar deposit in Pakistan, the former associated with initial rifting on the northern Gondwana margin in the Carboniferous, the latter associated with Gondwana rifting preceding break-up of Africa, India, and Australia.
The Sopokomil SHMS deposit (no. 1, Figs. 1, 4; Table 1) is located in northern Sumatra within the late Paleozoic basement that forms the spine of the island and which is extensively obscured by younger Mesozoic and Cenozoic sedimentary and volcanic rocks (Fig. 4). The deposit has been previously described by Middleton (2003). Mineralization at Sopokomil occurs in multiple strata-bound zones hosted by carbonaceous dolomitic shale and siltstone of the Julu unit, overlying dolomitized shelf carbonates of the Jehe unit and overlain by thin-bedded calcareous siltstones and wackes of the Dagang unit, which thicken and coarsen upward. Significant lateral thickness and facies variation within the Julu stratigraphy defines starved fault-controlled sub-basins with periodic influxes of coarser turbiditic sediment. The two principal sulfide bodies of Anjing Hitam and Lae Jehe (Fig. 4) occur within distinct sub-basins.
The footwall Jehe dolostones also host a significant but lower grade zinc-lead mineralization (ca. 5% combined) of cavity fill, vein, and replacement style. This mineralization has been partly oxidized and remobilized into shallow karst zones.
Strata-bound mineralization has been traced for a strike length of about 5 km, most of which is poorly tested by drilling. The mineralized trend runs along the northeastern side of the Sopokomil dome, an antiformal structure coincident with a magnetic high that may reflect an original basement high to the basinal host sequence.
The age of mineralization cannot be accurately constrained, but the textural and lithostratigraphic evidence suggests an early synsedimentary or syndiagenetic origin. The footwall carbonates are correlated with similar sequences in southern Sumatra with a Viséan (Early Carboniferous) fauna (Metcalfe, 1983; Fontaine and Vachard, 1984). Regional mapping previously assigned the Sopokomil sequence to the Carboniferous-Permian Tapanulli Group (Aldis et al., 1983). This group includes basinal sequences of wackes, mudstones, and glacial diamictites to the northwest of Sopokomil, probably younger than the Dagang unit wackes and representing Late Carboniferous to Early Permian glacially influenced sedimentation.
The host sequence to mineralization at Sopokomil is therefore interpreted to be late Early Carboniferous or early Late Carboniferous, deposited in a deepening cycle from platform carbonates to reduced, deep-water carbonaceous mudstones, and to thick turbidites and basinal mudstones. The setting is interpreted as an extensional rift-sag basin cycle without exposure of the basal rift sequence, with Sopokomil situated on a rift shoulder adjacent to a fault-controlled basement high.
The Duddar SHMS deposit in eastern Balochistan occurs within a north-south belt of Jurassic to Early Cretaceous carbonates and clastic rocks known as the Lasbela-Khuzdar belt #3, Figs. 1, 5; Table 1). This forms part of the thinskinned Balochistan fold belt along the northwestern margin of the Indian plate, formed during Paleogene collision with Asia. The Lasbela ophiolite belt to the west marks the zone of Neotethys Ocean closure.
Duddar is one of several strata-bound and vein-hosted zinclead-barite occurrences over a strike of several hundred kilometers, which includes the Gunga deposit (Fig. 5; Lydon, 1990). Mineralization is hosted by a sequence of argillaceous limestone and calcareous shale of the Late Jurassic Anjira Formation. These overlie platform carbonates of the Loralai Formation and basal transgressive conglomerate, arkosic sandstone, and interbedded shale and limestone of the Early Jurassic Spingwar Formation. The Anjira Formation is interpreted as a deep-shelf sequence overlying the Spingwar rift sequence and overlain by basinal sedimentary rocks of the Sember Formation (Skirka, 1998; Skirka et al., unpub. data).
Strata-bound sulfide mineralization at Duddar occurs within a dolomitic mudstone unit underlain by nodular argillaceous limestone and calcareous shale and overlain by deep-water argillaceous limestones with turbiditic horizons and debris-flow breccias. Mineralization occurs in different styles, including stratiform, stockwork, and breccia-hosted. Stratiform mineralization occurs in two principal horizons of barite and iron sulfide (pyrite or marcasite) with sphalerite and galena, from 2 to 30 m thick. The lower horizon is zinc rich, the upper dominated by barite and pyrite, which occur in mutually exclusive zones. Mineralization is commonly fine grained, laminated, and interbanded with mudstone and cherty gangue. Higher grade mineralization (ca. 8% Zn and 2% Pb) includes small-scale open-space fill textures with colloform sphalerite. Mineralization is associated with a range of iron and manganoan carbonate alteration in limestones.
A series of mineralized breccia beds overlie the stratiform mineralization, including sulfide and barite clasts in a mudstone matrix as well as sulfide-matrix breccias. Stockwork vein and disseminated sulfide and barite mineralization occurs in a discordant footwall zone, which cuts across and overprints stratiform mineralization. Stockwork mineralization is associated with quartz veining, is iron rich, includes colloform sphalerite, and contains more galena than the stratiform mineralization, as well as minor chalcopyrite.
Stratiform mineralization is interpreted to be broadly syngenetic to syndiagenetic. This is supported by sedimentary reworking of sulfide minerals, with strong fault control and early overprint by discordant mineralization which has many textural features characteristic of MVT and Irish-type deposits (Skirka, 1998).
Two significant MVT districts in northwestern Australia are associated with rift-sag cycles, similar to that interpreted at the Sopokomil deposit in northern Sumatra, but older. The Bonaparte basin underwent Late Devonian rifting with deposition of Frasnian sandstones and Famennian-Tournaisian sandstones and platform carbonates prior to deposition of Viséan sag-phase black shales (Gorter et al., 2005). The rift-sag cycle in the Bonaparte basin is slightly younger than the Givetian-Frasnian rifting in the Canning basin, which evolved to Famennian-Tournaisian sag phase deposition. The MVT mineralization on the Lennard Shelf in the Canning basin is earliest Tournaisian (Leach et al., 2000), and probably Tournaisian or Viséan in the Bonaparte Basin.
The Devonian is also a period of significant mineralization in the South China terrane, which at this time was located close to northern Gondwana. Large SHMS deposits occur in a Middle Devonian extensional sequence in the western Qinling belt on the northern margin of the South China terrane (Ma et al., 2004), while a suite of strata-bound zinc-lead deposits in the south of the terrane may also be related to rifting and extension (Shen, 1988).
The strata-bound Bo Hin Khao barite-zinc deposit in the Indochina terrane of northeastern Thailand shows characteristics of an SHMS system and occurs in host rocks of similar Carboniferous age to the Sopokomil deposit. The deposit is associated with a dolostone unit within a calcareous clastic sequence and is characterised by massive and finely banded barite with low-grade zinc (Suyasarote, 1994).
The Hakkari district in southeastern Turkey (#5, Fig. 1) has also been interpreted as a carbonate-hosted Jurassic-Cretaceous system of SHMS affinity (Yigit, 2009) and may be of similar age to Duddar. The deposit is located on the northern margin of the Arabian plate, south of the suture with the Anatolian terrane. Although mineralization is mainly oxidized, it is strongly strata bound within Jurassic carbonates and occurs at a similar stratigraphic position over a wide area. Minor sulfide mineralization comprises massive sphalerite-galena and banded pyrite.
VHMS and SHMS Mineralization Related to Neotethyan Convergence
Southeast Asia to Iran
Subduction commenced on the northern margin of Neo-tethys in the Late Triassic subsequent to the Indosinian and Cimmerian orogenies (Fig. 3). Through Tibet, Pakistan, and Afghanistan, the position of Neotethys is marked by the Indus-Yalu-Zangbo suture on the southern margin of the Lhasa terrane. The collision zone includes ophiolites, oceanic sedimentary rocks, and remnant Jurassic-Cretaceous arc and back-arc belts, such as the Kohistan-Ladakh, Xigaze, and Gangdese arcs that may have accreted to Eurasia before the Indian collision (Rolland et al., 2000, 2002). The West Burma and Sumatran Woyla terranes may also represent obducted arc and back-arc complexes (Barber, 2000; Barber et al., 2005).
Younger Mesozoic VHMS mineralization associated with Neotethys includes small occurrences in the West Burma and Woyla terranes (Barber et al., 2005). A more extensive copper-rich VHMS system occurs at Xiongun (#6, Fig. 1) in the Gangdese arc of southern Tibet (Qin et al., 2005). Mineralization occurs within a 2 km- × 200-m alteration zone in intermediate to mafic Cretaceous tuffs and includes a stratabound massive to banded sulfide and footwall stringer zone. The Gangdese arc formed during Cretaceous to Eocene northward subduction of the Indian plate and also hosts large porphyry Cu-(Mo-Au) deposits (Xietongmen) and associated polymetallic skarns (Beaudoin et al., 2005; Hou et al., 2009).
The Askot deposit (#7, Fig. 1) in northern India is interpreted as a VHMS deposit hosted by crystalline metamorphic rocks of uncertain age within a klippe near the Himalayan thrust front (Bowsell, 2006). The provenance is uncertain, but mineralization probably developed on the convergent northern Neotethys margin prior to Indian collision.
Iran to the Balkans
The history of convergence and back-arc rifting in western Neotethys (Fig. 3) is extremely complex. West of Iran, the effects of Cimmerian orogeny were more limited and Paleotethyan remnant oceanic basins such as Vardar reopened from Anatolia into the Balkans, broadly in a back-arc setting relative to the convergent Neotethys margin to the south and west (Stampfli and Borel, 2002). Large Kuroko-type VHMS deposits occur in this setting in the Pontide belt of northeastern Turkey (#8, Fig. 1). This is the only known Mesozoic Neotethyan VHMS district of real economic significance, and VHMS deposits also occur in the easterly continuation of the belt in the Caucasus. In contrast, Kuroko-type zinc-rich VHMS deposits are absent in the Late Cretaceous Balkan-Carpathian arc; this is dominated by porphyry copper and epithermal gold-copper mineralization with minor zinc and lead mineralization associated with subvolcanic intrusions.
Greater Caucasus belt: The Caucasus occupies a critical position on the Paleotethyan suture between Eurasia and the Cimmerian terranes to the south, reopened in a back-arc setting during Neotethyan subduction. Metallogeny is accordingly very variable and complex (Tvalchrelidze, 2009).
Economically the most important zinc mineralization in the Caucasus occurs in the Filizchai district, Azerbaijan (#4, Fig. 1), in a back-arc basin developed in the northern Greater Caucasus on the southern margin of Eurasia during the Jurassic (Buadze and Tvalchrelidze, 1980; Tvalchrelidze, 2009). Strata-bound mineralization is hosted by shales and graywackes, presumed to have been deposited in a deep-marine environment, in a sequence that also includes pillow basalts and other volcanic rocks. The orebody consists of a single horizon of massive sulfides comprising pyrite, sphalerite, galena, and chalcopyrite. Taylor et al. (2009) include Filizchai in their “clastic-dominated” classification based on host rock, and describe it as Sedex type.
Pontide belt: The Late Cretaceous to Eocene succession in northeastern Turkey and the Lesser Caucasus (Georgia, Armenia) is dominated by island-arc calc-alkaline volcanic sequences with a high proportion of felsic volcanics. Various tectonic scenarios have been proposed, but all relate to the subduction of Paleotethys under Eurasia (Robertson et al., 1995; Yilmaz et al., 2000), with possible complications related to back-arc rifting (Rice et al., 2006). Yigit (2009) maps over 30 VHMS deposits in the Turkish sector of this intensely mineralized terrane. Most of the deposits are copper dominant (Çağatay, 1993), such as Murgul where the mineralization is primarily in a footwall stockwork-vein system, but the worldclass Çayeli deposit (#8, Fig. 1), also known as Madenköy, and the smaller Lahanos and Koprubasi deposits are copper-zinc massive sulfides, often with economic gold and barite credits (Yigit, 2009).
VHMS mineralization in the Pontides is hosted by Senonian (Late Cretaceous) dacitic volcanic rocks and rhyolitic tuffs. The zonation and style of the alteration and mineralization have been compared to the classic Kuroko deposits by Çağatay (1993), Hobbs (2003), and Yigit (2009). The Çayeli deposit consists of at least two lenses of massive sulfides, as well as stockwork mineralization. Hobbs (2003) described four ore types, with zinc being particularly enriched in the “clastic” ore (average 13.6% Zn) and the “black” ore (11.55% Zn), both of which overlie the copper-rich “yellow” ore massive sulfide and “stockwork” zones.
The eastward extension of the Pontides in the Lesser Caucasus region is marked by VHMS and barite mineralization at Madneuli (#9, Fig. 1) in the Bolnisi district, Georgia (Migineishvili, 2001; Popkhadze et al., 2009). This complex deposit has been overprinted by gold-bearing epithermal mineralization and alteration. The original discovery outcrop consists of massive barite that was associated with a black ore type that overlies copper-dominant yellow ore.
Skarn-CRD and Epithermal Zinc-Lead Mineralization in Convergent and Collisional Arcs
Jurassic to Late Cretaceous in eastern Tethys
Only minor skarn and CRD (or manto) mineral occurrences are known in the arc belt from Sumatra to Tibet. This part of the northern Tethys arc was deformed and uplifted in the Late Cretaceous and is best preserved in tectonic slices on the southern Tibetan plateau, where small polymetallic skarns are associated with copper porphyry centers such as Xietongmen (Beaudoin et al., 2005).
The small Ganesh-Himal deposit (#19, Fig. 1) is located in high-grade metamorphic rocks in the Nepal Himalaya at an elevation of 4,420 m. The deposit has skarn mineralogy, but the age of formation is poorly constrained, and a Precambrian age has also been proposed (UN, 1993).
Minor epithermal and mesothermal base metal vein occurrences are also known in the remnants of the Jurassic to Cretaceous arc in Myanmar and Sumatra (Barber et al., 2009).
Late Cretaceous to early Cenozoic in western Tethys
Polymetallic mineralization at Shahumyan (#18, Fig. 1) in the Kapan district in the Lesser Caucasus of southern Armenia consists of steeply dipping quartz-carbonate-sulfide veins from which zinc, copper, gold, and silver are recovered. The mineralization is hosted by Late Jurassic dacites and andesites and is interpreted to be relatively deep level epithermal style. The district also contains possible VHMS and porphyry copper-dominant mineralization (Mederer and Moritz, 2009).
In the Turkish Tauride block, Soylu (2003) and Boztuğ et al. (2003) reviewed zinc-lead-copper skarn mineralization that is related to Late Cretaceous to Paleogene calc-alkaline magmatism associated with the back-arc collision of the Cimmerian terranes in central Anatolia with the Eurasian plate to the north. Skarn mineralization is exploited at Çadirkaya, where the mineralization is clearly related to the contact between granodiorite and shelf carbonates. The sulfide mineralization transitions upward into oxide mineralization.
Other skarn-type deposits related to possible Cretaceous granitic intrusions include the Akdağ district (Vaché, 1963) and the Keban deposit in the eastern Taurides (Yilmaz et al., 1992). Keban is hosted by Paleozoic marbles and is related to a Late Cretaceous or Eocene syenite porphyry intrusion that produced exoskarn in the adjacent marbles. Mineralization consists of small strata-bound lenses of sphalerite, galena, pyrite, and chalcopyrite that have been locally oxidized in karst-enhanced fractures.
Late Cretaceous magmatism in the Balkan-Carpathian arc is dominated by porphyry copper and epithermal gold-copper mineralization in the Banat (Romania), Timok (Serbia), and Srednogorie (Bulgaria) magmatic complexes. Zinc- and lead-rich deposits occur, for example, as relatively minor skarns in marbles and limestones peripheral to the major Majdenpek andesite-hosted copper porphyry system in eastern Serbia (Jelenković and Koželj, 2002, Krstić et al., 2002) and in the Banat district (Ciobanu et al., 2002). The Eocene porphyry copper-gold mineralization at Recsk (Hungary) is associated with zinc skarn mineralization in Cretaceous carbonates peripheral to porphyry copper mineralization.
Oligo-Miocene collisional arc belts
Late Cretaceous to Cenozoic closure of ocean basins in the western Neotethys is marked by a series of ophiolite belts in prominent tectonic suture zones such as in the Balkans (Vardar Zone) and Turkey (Izmir-Ankara suture). Closure along the Alpine-Carpathian-Anatolian belt in the Late Cretaceous was followed by postcollisional extension in the Oligocene and Miocene and initiation of subduction of oceanic crust in the eastern Mediterranean. This was accompanied by calc-alkaline and alkaline magmatism which was associated with base and precious metal mineralization, including formation of some important zinc-lead and silver-zinc-lead deposits. The Balkan zinc-lead belt (Fig. 6) extends from Slovakia, through Romania, Serbia, and Kosovo, Macedonia and northern Greece into southern Bulgaria and Turkey (Heinrich and Neubauer, 2002). The belt has a long history of mining, dating back to the Romans and has been a significant metal producer in modern times.
Subduction rollback in the western Mediterranean resulted in Miocene collision with the African passive margin and formation of the Atlas fold and thrust belt (Fig. 7) which continues into Spain as the Betic belt (Rosenbaum et al., 2003). Miocene to Pliocene magmatism in the Atlas belt is associated with slab break-off and extensional collapse. Collision between Arabia and Iran along the Taurus-Zagros belt also culminated in the Miocene as convergence between Africa and Eurasia continued.
The various styles of zinc-lead mineralization in these Neotethyan districts (Fig. 7), of which selected examples are described in more detail below, include the following: (1) skarn, CRD, and vein mineralization, usually proximal to a subvolcanic intrusive body and typified by the Kopanoik (or Trepča) district (Serbia and Kosovo, #11, Fig. 1), Sasa (Macedonia, #13, Fig. 1), the Kassandra district (northern Greece, #14, Fig. 1), the Balya district (northwestern Turkey, #17, Fig. 1), and the La Union district (southeastern Spain, #10, Fig. 1); and (2) base metal-rich epithermal mineralization, usually as veins that are spatially associated with Oligocene and Miocene intermediate to felsic subvolcanic and volcanic rocks, typified by the Hodrusa district (Slovakia), Srebrenica (or Sase, Bosnia-Herzegovina, #12, Fig. 1), Kratovo-Zletovo (Macedonia, #13, Fig. 1), and Baia Mare (Romania) deposits.
Serbia and Kosovo: The Kopaonik district in Serbia and Kosovo (Jankovic et al., 1997) includes five zinc-lead deposits that were mined until 1999 as well as a number of minor occurrences (Fig. 6). Most deposits are associated with contacts of Miocene quartz diorite intrusions with Triassic or Late Cretaceous carbonate rocks. Favorable settings include stratigraphic or structural contacts between carbonates and other rock types, or penetrative structures in amphibolites and serpentinized peridotite rocks. The Stan Terg-Stari Trg and Belo Brdo deposits formed as CRD in Triassic limestone, whereas Kishnica, Crnac, and Ajvalija occur as quartz-carbonate-sulfide epithermal vein deposits. The most common controls on base metal mineralization in the Kopaonik district include the following: regional north-northwest−trending faults of the Vardar one, local congruent folds or connecting faults, and local spatial association with Cenozoic intermediate to felsic alkali intrusions or subvolcanic stocks.
Modern mining commenced in 1930 at the Stan Terg-Stari Trg zinc-lead deposit, which is also known as the Trepča deposit. The geology of the area is characterized by a cover of Neogene andesite and dacite pyroclastic and volcanic rocks that overlie a Triassic sequence of schists, quartzites, and marbles, Jurassic mafic volcanic rocks, and serpentinized intrusions and diabase. Major northwest-trending faults parallel regional strike of the pre-Cenozoic geology. The mineralization occurs as a number of individual orebodies that are by discontinuous lenses of Triassic limestone and is overlain by a black schist (Forgan, 1948). These mineralized limestones extend along a strike length of 1,200 m and have explored to a depth of 925 m. The structure is complex, consisting of an anticline plunging at about 40° NW. A breccia pipe consisting dominantly of andesite and dacite clasts, including schist, quartzite, and limestone fragments, follows the hinge of the plunging anticline. The massive sulfide replacement mineralization occurs in a number of garnet-epidote-magnetite skarn lenses in the carbonates at the contact or close to, the breccia. The ore mineralogy of the deposit is dominated by pyrite, pyrrhotite, sphalerite, and galena, with sparry calcite and quartz gangue. In detail the mineralogy is varied and includes minor amounts of chalcopyrite, enargite, magnetite, stibnite, and arsenopyrite. The Ajvalija deposit consists of a series of lenses along a strike of 300 m and downdip extensions of as much as 700 m. Intensely deformed limestone and marble within the Paleozoic schist and phyllite succession host the sulfide mineralization. The mineralization is particularly well developed in the hinges of folded carbonates within an anticline plunging approximately 20° SE, which is bounded by a western reverse fault that is marked by breccias, possibly a feeder for hydrothermal solutions, and an eastern fault, both dipping steeply to the northeast. Ajvalija is the only major deposit in the Kopaonik district that is not spatially associated with Cenozoic volcanic rocks. The schists and phyllites are hydrothermally altered, with common silicification and chloritization adjacent to the mineralization.
The Belo Brdo deposit includes vein and skarn mineralization in addition to the dominant CRD mineralization (Veselinovic-Williams et al., 2007). The geology of the deposit area consists of Triassic metamorphic rocks, serpentinites, and Cretaceous limestones in fault contact and overlain by Cenozoic clastic, volcaniclastic, and volcanic rocks. The deposit is cut by a number of quartz-latite dikes. Replacement mineralization is located on or close to the tectonized contacts of Triassic and Cretaceous carbonates with volcaniclastic rocks and/or serpentinite. The ore mineralogy is complex and is dominated by pyrite, sphalerite, and galena, with lesser arsenopyrite, chalcopyrite, and sulfosalts. Quartz and manganoan calcite are the main gangue minerals. Vein mineralization consists of a single quartz-carbonate-sulfide vein with a strike of 400 m. It penetrates into the overlying Cenozoic volcaniclastic rocks. Skarns are developed in Cretaceous carbonate and consist of magnetite, pyrrhotite, galena, sphalerite, and chalcopyrite.
The Lece zinc-lead deposit is the most important occurrence in the Miocene Lece magmatic complex, which is located east of the Kopaonik district (Fig. 6). The mineralization consists of sphalerite-galena-pyrite and quartz in structurally controlled breccia zones that are up to 2 km long and 10 m wide. The low sulfidation mineralization was exploited for zinc (2.5% Zn) and lead (1.7% Pb) and is associated with significant gold content (4 g/t Au; Jankovic, 1982).
Macedonia: The Sasa deposit in Macedonia includes Svinje Reka, which is described as a classic strata-bound metasomatic-replacement (Serafimovski and Aleksandrov, 1995) or CRD-skarn deposit (Canby et al., 2003). The host rocks include marbles interlayered with quartz-graphite schists of pre-Mesozoic age that belong to the Cimmerian Serbo-Macedonian massif (e.g., Şengör et al., 1984). Garnet, ilvaite, and epidote skarn mineralogy is developed in the marbles surrounding an Oligocene-Miocene quartz-diorite intrusive complex that hosts porphyry-style copper mineralization. The nearby mine at Toranica exploits smaller lenses of similar mineralization (Serafimovski and Aleksandrov, 1995).
The Kratovo-Zletovo zinc-lead district in Macedonia surrounds another Miocene calc-alkaline magmatic complex. Galena- and sphalerite-bearing quartz veins, probably intermediate sulfidation epithermal types, are exploited at the Zletovo deposit and are controlled by fracture zones in the dacitic ignimbrite host rock (Serafimovski and Aleksandrov, 1995). The alteration is characterized by silicification and argillization, and sulfide assemblages, including a high-sulfidation copper-gold overprint at the nearby Plavica deposit (Alderton and Serafimovski, 2007).
Romania: The historically important Baia Mare district in northern Romania contains a number of epithermal polymetallic epithermal deposits related to a major east-west strike-slip fault zone and Miocene calc-alkaline magmatism. Kouzmanov et al. (2005) list seven ore deposits with resources in the district. The tectonic evolution of this section of the Carpathian arc is very complex, and Grancea et al. (2002) suggested that it is related to subduction roll back and break-off of the descending plate. The deposits consist primarily of veins, with subordinate breccias pipe and stockwork veinlets, representing low- to intermediate-sulfidation mineralization (Kouzmanov et al., 2005). Although the frequency of mineralization in the district is widespread, the individual orebodies tend to be small (less than 10 Mt) with low base metal grades (e.g., one of the largest deposits is Suior, with 9.3 Mt at 2.3% Zn, 1.4% Pb, 0.6% Cu, 29 g/t Ag, and 0.4 g/t Au).
Bulgaria: The Rhodope massif is the eastern extension of the Serbo-Macedonian massif and hosts several small low-grade base metal mines (Marchev et al., 2005; Marchev, 2007) of which the Madan district deposits are the best described. Mineralization occurs as structurally controlled northwest- to north-northwest−trending epithermal vein systems cutting Precambrian basement gneiss and marble and as strata-bound skarn-like replacements within marble (Vassileva et al., 2005). The veins comprise quartz-carbonate-sulfide assemblages exhibiting massive, banded and brecciated textures, whereas the skarns are dominated by a gangue of johannsenite-rhodonite-quartz. The mineralization has been dated at 30.6 to 30.0 Ma and is related to Oligocene felsic-intermediate dikes that cut the basement and overlying felsicintermediate ignimbrites (Vassileva et al., 2005).
Greece: Two important zinc-lead districts in Greece, Lavrion near Athens and Kassandra on the Chalkidiki peninsula, east of Thessaloniki (Fig. 6), are genetically related to Miocene magmatism (Forward, 2007; Skarpelis, 2007).
The Olympias and Stratoni (Madem Lakkos) zinc-lead deposits in the Kassandra district (#15, Fig. 1; Forward, 2007), which is also known for the Skouries porphyry copper-gold deposit, are hosted by metamorphic rocks of the Serbo-Macedonian massif. The metamorphic basement is intruded by the 30 Ma Stratoni granodiorite and the 20 Ma Skouries syenite porphyry. Olympias and Stratoni are strata-bound CRDs hosted by marble horizons in the metamorphic basement, with local thickening of the mineralization where marble is thickest in fold closures. The mineralogy of both deposits is dominated by sphalerite, galena, and pyrite, with significant arsenopyrite at Olympias which also has a relatively high precious metal content. Fluid inclusion as well as lead and sulfur isotope data are indicative of a magmatic origin for the relatively high temperature (300°–400°C) mineralizing fluids (Kalogeropoulos et al., 1989).
The historically famous Lavrion zinc-lead district (#15, Fig. 1) is located within the structurally complex Attic-Cycladic belt that includes a number of skarn and epithermal deposits of Miocene age in the western Aegean (Skarpelis, 2007). At Lavrion, interlayered thrust sheets of Triassic clastic rocks and marbles, blueschist-facies clastic rocks, mafic rocks, and Late Cretaceous limestones are intruded by a Miocene granodiorite stock. Exoskarns with magnetite and silver-rich zinclead-sulfide mineralization occur at the contact of the granodiorite with the carbonate units, but the bulk of the Lavrion deposits occur as strata-bound bodies of galena and sphalerite replacement mineralization and, to a lesser extent, structurally controlled carbonate-fluorite veins. Skarpelis (2007) interprets these to be Miocene replacement deposits formed during postcollisional back-arc extension in the Aegean. The Lavrion deposits were subject to intense supergene oxidation with the formation of economically significant nonsulfide zinc mineralization (Skarpelis and Argyraki, 2008).
Turkey: A number of small CRD zinc-lead deposits associated with Oligocene-Miocene subvolcanic dacitic and andesitic intrusions occur in the northwest of the Turkish peninsula (Yigit, 2009). The Balya deposit (#17, Fig. 1) is one of the most significant and has past production of at least 4 Mt (Table 1; Agdemir et al., 1994). The CRD mineralization, locally with skarn mineralogy, is mostly hosted by Permian and Triassic limestones at or close to contacts with dacite stocks and dikes. The magmatic rocks are intensely altered, and the mineralization has been interpreted by Agdemir et al. (1994) to be indicative of an epithermal environment.
Betic belt, Spain: The Cenozoic volcanic province in the western Mediterranean runs from the Balaeric islands to the Betic belt of southeastern Spain and continues as the Rif of northern Morocco and the Kabylies of Algeria. In Spain the magmatism consists of calc-alkaline and alkaline volcanic rocks, shoshonites, and subvolcanic intrusions related to postcollisional extension in the Betic cordillera (Lopez-Ruiz et al., 2002). This intensely mineralized district includes epithermal gold mineralization at Rodalquilar as well as significant zinclead mineralization at La Union (#10, Fig. 1), with a 2,000-year history of mining.
The mineralization at La Union occurs mostly as carbonatereplacement bodies with sphalerite, galena, and pyrite in Triassic limestones (Oen et al., 1975; Manteca and Ovejero, 1992). The mineralization is zoned and centered around Miocene trachy-andesitic volcanic rocks and subvolcanic intrusions, which themselves contain veins of zinc-lead sulfide and barite mineralization and are intensely altered with a high-sulfidation assemblage. Sulfide and oxide mineralization was also exploited from the Miocene sedimentary rocks that fill small, postcollisional sedimentary basins that developed during the volcanism. The variety of mineralization styles, as well as the alteration and the clear association with Miocene volcanism, points to carbonate replacement in a high level, epithermal environment. A similar relationship between mineralization in basement, volcanic, and Miocene shallow-marine sediments is described by Lopez-Gutierrez et al. (1993) from the Vera-Garrucha area and other extensional Neogene sedimentary basins in the Betic cordillera.
MVT Mineralization in Carbonate Platforms on Passive Margins
Thick successions of Mesozoic platform carbonates extend from western Europe through the Dinarides of the Balkans into central Anatolia, Turkey, and central Iran. In Anatolia and Iran, Jurassic-Cretaceous molasse deposition following Cimmerian orogeny was followed by Cretaceous to Cenozoic carbonate deposition as extension and transgression resumed. Similar thick Mesozoic to Paleogene shelf carbonates were deposited on the southern Tethyan passive margin through North Africa and the Middle East.
Extensive MVT zinc-lead mineralization occurs in the platform carbonates of the Neotethyan belt (Fig. 7). Whereas most of these deposits are interpreted to have formed during Cenozoic compression and uplift accompanying Neotethys closure along the greater Alpine-Himalayan orogenic belt, some may have formed in carbonate platforms at an earlier stage of basin evolution.
Alpine zinc-lead province
Strata-bound carbonate-hosted zinc-lead mineralization is common in the Triassic carbonates of Alpine Europe (#20–23, Fig. 1), where it is best described at the Bleiberg (Austria), Raibl and Salafossa (Italy), and Mezica (Slovenia) deposits (Leach et al., 2003; Schroll, 2005). The mineralogy is dominated by sphalerite and galena with fluorite, some barite, and pyrite. The mineralization includes strata-bound replacement of favorable lithologic units within Middle Triassic limestones and dolomites, as well as discordant veins and karst-cavity fillings.
Many authors argue that the mineralization is essentially MVT (e.g., Leach et al., 2003). There is a clear structural control to the distribution of the host carbonate lithologic units and facies, which reflect a shallow-marine to lagoonal environment, manifested by faults that were active during sedimentation of the host sequence and reactivated during the Late Triassic and Early Jurassic, and then again during the Cenozoic Alpine deformation. The relationships between early saddle dolomite and the sulfide mineralization suggest that the mineralization most likely occurred during the Late Triassic to Early Jurassic extension event (Leach et al., 2003).
The Basque-Cantabrian basin developed initially through Triassic rifting with deposition of red beds and evaporites overlain by Jurassic to Cretaceous platform carbonates and clastics (Grandia et al., 2003). It developed contemporaneously with Atlas rifting to the south as the Neotethys Ocean opened westward in the early Mesozoic. The basin was inverted and closed during Late Cretaceous Pyrenean convergence.
There are numerous zinc-lead occurrences in the basin, including three that have been mined, the world-class Reocín and smaller La Troya and Legoretta deposits (#24–25, Fig. 1; Table 1), all hosted by Aptian carbonates of the Urgonian cycle. This clastic-carbonate platform succession overlies Triassic to Jurassic red beds and evaporites which have been emplaced as salt diapirs along basin-controlling faults. The sulfide mineralization consists of sphalerite, galena, pyrite, and marcasite and is typically strata bound in Urgonian carbonate facies. Many of the sulfide occurrences have been oxidized by circulating meteoric waters in karst systems.
Massive pyrite-sphalerite horizons associated with sideritization are reported from La Troya by Fernàndez-Martinez and Velasco (1996). There is a clear metal zonation vectoring toward faults that are interpreted to have been active as feeders at the time of mineralization.
At Reocín mineralization is replacement and cavity-fill style within dolomitized host rocks and interpreted to be partly hosted by paleokarst related to Cenomanian emergence (Velasco et al., 2003). The distribution of the host Urgonian carbonate facies is controlled by synsedimentary faults that also control the intensity of dolomitization and mineralization.
The age of the mineralization remains controversial. The La Troya deposit displays many features indicative of mineralization soon after deposition of the host rocks, and Fernàndez-Martinez and Velasco (1996) interpreted the metal ratio distribution in terms of three exhalative pulses. The more clearly MVT-style mineralization at Reocín has been related to Paleocene basin inversion and compression (Velasco et al., 2003) or middle Miocene compression and uplift, based on paleomagnetic dating (Symons et al., 2009). Mineralization has been interpreted to result from mixing of basinal brines and fluids derived from evaporite dissolution (Grandia et al., 2003).
The Mesozoic and Cenozoic platform carbonates of the Atlas belt, from Tunisia through Algeria and to Morocco, host extensive zinc-lead mineralization. Whereas most MVT mineralization is related to Atlas orogenic compression and uplift, the Bou Grine deposit in Tunisia has also been interpreted to be syngenetic to syndiagenetic and related to salt diapirism (Rouvier et al., 1985; Orgeval, 1994).
The Bou Grine deposit is hosted by Turonian carbonates on the margins of the Lorbeous Triassic inlier, comprising sediments and gypsiferous breccias interpreted to be emplaced as a salt diapir controlled by northwest-oriented fault zones (Schmidt, 1999). The bulk of mineralization occurs within a small, high-grade breccia zone of typical MVT character interpreted to be of hydrothermal karstic origin. Significant mineralization also occurs strata bound within a strongly organic limestone (Early Turonian “Bahloul” facies) underlying the breccia zone, and minor mineralization occurs in breccias in the margin of the diapir.
Mineralization at Bou Grine has been interpreted as syngenetic and related to fluid flow controlled by salt diapir emplacement during sedimentation (Orgeval, 1994). However, there is no direct control on the age of mineralization, and the karstic breccia mineralization occurs in clean limestone above the strata-bound zone, capped by Aleg facies calcareous mudstones and limestones of Santonian age. Mineralization in the Bahloul facies occurs as veinlets following a steep fabric that has been compressed vertically. This texture was interpreted by Orgeval (1994) to reflect precompactional veining, but a later origin during lateral compression is also possible. Minor mineralization in Miocene rocks in the vicinity of Bou Grine may point to an entirely Neogene mineralization event.
On the southern edge of the Tunisian Cretaceous basin, strata-bound zinc-lead mineralization in Aptian dolostones is widely developed close to a major fault system that controlled Albian basin development. The setting and style of mineralization show strong similarities to the deposits of the Basque-Cantabrian basin, but only small deposits have been exploited to date.
A number of zinc-lead-barite occurrences are hosted by Late Jurassic carbonates in southwestern Yemen (#27, Fig. 1), associated with regional northwest-trending fault systems (Al Ganad et al., 1994). The host Jurassic platform carbonate sequence covers much of the southwestern Arabian peninsula in Yemen, deposited on the southern passive margin of Neotethys. The host carbonates consist of dolomitized bioclastic limestones, located on the flanks of a sedimentary basin filled with pelites and evaporites. The sequence is intruded by lower Miocene trachyte sills and dikes.
The Jabali deposit is the most significant economically and has been described by Christmann et al. (1983) and Al Ganad et al. (1994) as being hosted by fractured, dolomitized, and karstified limestones with crude strata-bound morphology. Most of the mineralization consists of nonsulfide zinc minerals that accumulated in karst cavities, with only minor remnant sphalerite, galena, and pyrite. Al Ganad et al. (1994) discussed a complex genetic history associated with active faulting on the basin margin, as well as dolomitization and karstification of the host limestones.
MVT Mineralization in Collisional Fold and Thrust Belts and Orogenic Forelands
Neotethys evolved in the Late Cretaceous and Tertiary from a complex collage of cratonic blocks, arcs, and back-arc basins to the present-day assemblage of collisional orogens, foreland basins, and remnant ocean basins. Widespread MVT zinc-lead mineralization resulted from large-scale fluid-flow systems dominated by basinal brines, driven by inversion, compression, and closure of deep sedimentary basins and tectonic uplift of orogenic belts. Generation of regionally significant zinc-lead districts was facilitated by the prevalence of Mesozoic carbonates deposited on continental platforms marginal to Neotethys.
Most of the Neotethyan MVT districts occur within orogenic belts, whether formed within the orogens or subsequently incorporated in advancing fold-and-thrust belts. Some occur in classic foreland basin settings, notably the Silesia and Cevennes districts. In the Atlas belt, deposits occur within the orogen and in the foreland.
Upper Silesia, Poland
A number of zinc-lead deposits occur in the Middle Triassic “Muschelkalk” in the relatively flat lying sequences of the Alpine foreland in Germany and Poland. Most are small except for the zinc-lead deposits in the Upper Silesia district, Poland. Upper Silesia is the largest MVT district in the world with an estimated global resource (past production and reserves) of 731 Mt at grades of 4.24 percent Zn and 1.34 percent Pb according to Taylor et al. (2009). The deposits occur in four clusters, each of which is 5 to 15 km2 in area, and the whole district covers an area of approximately 50 by 40 km. The Pomorzany mine is the remaining principal producer in the district. The Upper Silesia district also contains significant resources of nonsulfide mineralization (locally known as galmei, or calamine), which was formed by supergene oxidation of the primary sulfide zinc during the complex interplay of uplift and karstification (Boni and Large, 2003).
In Upper Silesia, the ore-hosting limestones were deposited in a shallow-marine, locally evaporite-bearing, tropical environment that was developed on the northern margin of the Tethys Ocean (Szulc, 2007), when Permo-Triassic rifting and extension propagated westward with Pangea breakup. The Upper Silesian zinc-lead mineralization consists primarily of tabular breccias, cavity-fill, and replacement bodies broadly strata bound within dolomitized Middle Triassic Muschelkalk limestone, locally known as the “ore-bearing dolomite” in the Gogolin beds (Sass-Gustkiewicz, 2007). Sphalerite and galena are the dominant sulfides. The mineralized breccias are cemented by sulfides, and Sass-Gustkiewicz (1996) proposed a hydrothermal origin for the brecciation and karst features, whereas Leach et al. (2003) argued for a meteoric premineralization origin of the karst collapse breccias. The age of the dolomitization and mineralization is also controversial. Although there are geologic and spatial indications that at least some mineralization formed pre-Jurassic (e.g., Sass-Gustkiewicz and Kucha, 2005), Bradley and Leach (2003) presented geologic interpretation and paleomagnetic data to argue that the mineralization occurred during the Cenozoic uplift of the northern Carpathians and compared the setting to that of the Southeast Missouri district with respect to the uplift in the Ouachita orogen.
The MVT deposits of the Cevennes district (#29–30, Fig. 1) in the southern Massif Central of France had a long history of exploitation, finally ceasing production in 1992. Les Malines and L’Argentière deposits were developed as the most substantial modern mines. Mineralization at Les Malines is mainly hosted in karst systems that formed in metamorphosed Cambrian dolostones following Hercynian orogeny and uplift, prior to deposition of Jurassic passive margin carbonate-shale cycles (Ramboz and Cheref, 1988). Mineralization comprising colloform sphalerite with galena, quartz, barite, and dolomite occurs as open-space and fracture fill within the karst zones. Pyrobitumen is common, and chalcopyrite and tetrahedrite-tennantite are locally present. Vein mineralization also occurs in Triassic shales above the unconformity. Paleomagnetic dating suggests a late Paleocene to early Eocene age of mineralization (Leach et al., 1998, 2001a, b), which is coincident with clastic sedimentation in foreland basins north of the uplifting Pyrenean and Alpine orogens (Bradley and Leach, 2003).
The regionally extensive carbonate-hosted zinc-lead deposits of the Atlas belt of northern Africa have supported mining since the Phoenicians but most known occurrences are small and few significant modern mines have been developed. Mineralization is hosted by extensive Jurassic to Eocene passive-margin platform carbonates, which overlie rift-cycle red beds and evaporites of Triassic age. The Triassic evaporites have been widely mobilized as diapiric intrusions (Perthuisot et al., 1999), controlled largely by basin architecture faults. Significant mineralization also occurs within diapiric cap-rock breccias.
The enormous extent of mineralization suggests a regional-scale fluid-flow event. The Miocene Atlas orogeny reflects collision of the Rif-Kabylie arc with the North African passive margin (Rosenbaum et al., 2003) and resulted in development of a broad foreland fold and thrust belt with the upper nappes emplacing deep-water carbonates and clastic rocks from the north (Rouvier, 1977). Miocene-Pliocene extensional collapse was associated with dextral strike-slip displacement on crustal-scale northeast-trending faults and opening of pull-apart basins mainly filled by continental sedimentary rocks, including lacustrine limestones. Basin-brine migration could have accompanied early Atlas basin inversion and compression in the Late Cretaceous or Paleogene (Clayton and Baird, 1997). However, the common occurrence of zinc-lead mineralization in both pre-nappe Eocene-Oligocene and postnappe Miocene sedimentary rocks indicates a significant younger Neogene mineralization event with fluid flow driven by Atlas compression and uplift.
The Touissit-Bou Beker deposit (#31, Fig. 1), located mainly in Morocco but extending across the border into Algeria (where it is known as El Abed), is the largest MVT deposit in the Atlas belt, with a global resource of 67 Mt at 7 percent Pb and 3 percent Zn (Table 1). Mineralization is broadly strata bound within Middle Jurassic dolostones, which are overlain by Middle to Late Jurassic marls and sandstones on a Paleozoic basement high (Rajlich, 1983). Mineralization is mainly open-space fill style in karstic breccias and veins; fault control is significant, but the irregular geometry of ore zones suggests a predominant karstic control. The deposit is zoned from lead rich in the west to more zinc rich in the east. Chalcopyrite is also present, and the deposit had economically recoverable silver. On a regional scale, the deposit occurs near the northern margin of the Oran Meseta, in the foreland of the Middle Atlas-Tell Atlas fold belt to the north (Fig. 7). Mineralization is interpreted to result from fluid flow driven by Oligocerne-Miocene Atlas compression and uplift, with sulfur sourced from local Triassic evaporites (Bouabdellah et al., 1999).
The Touissit-Bou Beker deposit provides a good example of an Atlas MVT in a foreland setting. Many other Atlas MVT deposits occur within the fold-and-thrust belt and include cavity fill and vein styles as well as deposits hosted in diapir cap rock such as Fedj el Adoum in Tunisia (Fig. 7). Although many small mines have operated until recent times, no large deposits have been discovered.
Thick sequences of late Paleozoic and Mesozoic carbonates were accumulated in the Taurides of central Turkey and are the host to several districts of zinc-lead mineralization, with the Yahyali or Zamanti district (#32, Figs. 1, 7) being one of the most important (Yigit, 2009). The geology of the Zamanti district is dominated by a thick, Late Devonian to Early Cretaceous sequence of shelf carbonates intruded by Cretaceous granitic and intermediate magmatic rocks (e.g., Ceyhan, 2003). According to Stampfli (2000), this sequence accumulated on the Menderes-Taurus block of the Cimmerian terrane, on the southern marginal platform of Paleotethys. The complexity of the tectonic history is illustrated by the conflicting interpretations: according to Kuscu et al. (2007), collision occurred during the Late Cretaceous, resulting in intense compressional tectonism, thrusting, and uplift of the Anatolian Tauride block, whereas Stampfli (2000) considers that collision occurred earlier in the Jurassic.
In this district, nonsulfide zinc mineralization, predominantly smithsonite and hydrozincite, and lead mineralization as cerussite with traces of relict galena are exploited at Delikkaya from fracture- and cavity-fill zones and from a complex paleokarst system in Devonian limestones. There have been several phases of erosion and karstification during the Jurassic and Cretaceous, and subsequent to the Late Cretaceous deformation. Mineralization is broadly strata bound but also occurs as crosscutting breccias within the host lithology. Similar deposits to Delikkaya (e.g., Kaleköy, Denizovasi, Tekneli) are described from the region by Koptagel et al. (2005) and Çevrim (1984), who concluded that the primary mineralization in the district is carbonate replacement followed by karst infill. The age of the primary sulfide mineralization is not known. The mineralization can be generally described as MVT with a late-stage karst modification and remobilization of the nonsulfide phases during the Cenozoic.
Several large, carbonate-hosted zinc-lead deposits occur in central Iran (#33–35, Fig. 1), notably the Iran Kuh and Mehdi Abad deposits that are hosted by Early Cretaceous shelf limestones on the Cimmerian Yazd-Lut block (Fig. 7). Following Jurassic collision and uplift accompanying closure of the Paleotethys Ocean, renewed extension in the Cretaceous from Iran to Turkey resulted in transgression and carbonate deposition, continuing into the Paleogene. Inversion and uplift accompanied convergence and collision with Arabia in the Oligocene, with central Iran in the foreland of the Zagros fold belt (Fig. 6).
Mineralization at Mehdi Abad (Fig. 7) is broadly strata bound in the hanging wall of the Black Hill fault. Mineralization is predominantly dissolution cavity- and breccia-fill comprising sphalerite, galena, and barite with minor pyrite, and significant chalcopyrite, particularly in fault zones (Chapple, 2003). Mineralization is associated with iron carbonate alteration of dolomitized carbonates of the Early Cretaceous Taft Formation that overlie Jurassic basement, which was deformed and intruded by granite during the Cimmerian orogeny. The Taft Formation is a thick-bedded shelf limestone overlying shallow-water oolitic limestones, sandstones, and basal conglomerate. It is overlain by deep-water cherty limestone and shale. To the north, Early Cretaceous basinal flysch sediments with calciturbidites are at least partly laterally equivalent. About one-third of the deposit has been completely or partly oxidized with karst overprint.
Iran Kuh (Fig. 7) occurs in a similar transgressive Early Cretaceous carbonate sequence, hosted by dolomitized and brecciated limestones overlain by Albian shales. The morphology of the sulfide mineralization is described by Ghazban et al. (1994) as lenses of strata-bound open-space fill and is dominated by sphalerite, galena, and pyrite, with barite and oxidized zinc minerals. Mineralization at Iran Kuh has been interpreted to be controlled by a major fault which introduced basinal brines (Ghazban et al., 1994).
There is no direct age control on the Iranian deposits. The mineralization is most likely generated by fluid flow driven by inversion, compression, and uplift in the Sanandaj- Sirjan belt caused by Paleogene convergence and Oligocene collision with Arabia from the south.
A number of late Mesozoic to Cenozoic MVT districts and deposits in Southeast Asia and in the Himalayan foreland (Fig. 8) can be related to collision of the Lhasa-West Burma and Indian terranes with Asia in the Late Cretaceous to Neogene.
The Padaeng deposit (#36, Fig. 1, Table 1) is the largest known MVT system in Southeast Asia. Padaeng is hosted by Early Jurassic carbonates, deposited in a transgressive marginal to shallow-marine environment following Late Triassic Indosinian orogeny. The Jurassic sequences were deformed and uplifted during the Late Cretaceous collision with the West Burma terrane and are poorly preserved. Padaeng is one of the largest exploited nonsulfide zinc deposits; its setting and relationships to nearby sulfide mineralization clearly point to Neogene supergene modification of hypogene MVT mineralization associated with hydrothermal ferroan dolomitization of favorable carbonate units (Reynolds et al., 2003). Hypogene MVT mineralization is interpreted to have formed from regional-scale fluid flow driven by Late Cretaceous orogeny. However, mineralization at Padaeng occurs within a major northwest-trending fault zone, one of a set of structures that accommodated Eocene to Miocene extrusion of Southeast Asia in response to Indian collision (Tapponier et al., 1982), and a later formation related to this event is also possible.
A number of smaller deposits occur in the extensive Permian-Triassic dolomitized platform limestones of the Shan plateau, the cratonic core of the Shan-Thaui block in Myanmar and western Thailand, notably the Long Keng smithsonite deposit (Fig. 8; Hitzman et al., 2003). This region of eastern Myanmar is very poorly known.
Hybrid Zinc-Lead Deposits
Hybrid zinc-lead deposits in the Tethyan belt include those for which there is an obvious magmatic influence, possibly as a heat engine for circulating mineralizing fluids, but also good evidence for a basinal brine origin of the mineralizing fluids. Examples of deposits with hybrid characteristics occur in the Atlas belt of North Africa, in Iran, and in the Himalayan foreland in southwestern China (Figs. 7, 8).
The large Oued Amizour deposit (#37, Figs. 1, 7; Table 1) in northern Algeria is hosted by Miocene potassic calc-alkaline volcanics in the Kabylie belt. The host sequence includes andesitic and dacitic volcaniclastic breccias, lavas, and subvolcanic intrusions. Mineralization occurs as a thick discordant zone from 40 to 300 m thick, broadly controlled by a shallowly south dipping fault, and associated with variable degrees of sericitic and kaolinitic alteration. Adularia is also reported. Mineralization includes semi-massive sulfide, stockwork, breccia-hosted and disseminated styles. Mineralization is characterized by low iron colloform sphalerite with galena and pyrite. Silver and arsenic values in the main Tala Hamza body that hosts the published resource (http://www.terramin.com. au) are low and gold is not anomalous. Recent drilling has encountered narrower zones of silver-rich mineralization (as much as 373 g/t) in the downdip southern extension of the deposit.
The Sidi Driss deposit (#38, Figs. 1, 7) in northern Tunisia is hosted by Late Miocene sedimentary and epiclastic rocks in the Sedjenane basin adjacent to the Oued Belif volcanic-intrusive complex (Decrée et al., 2008). Mineralization comprises galena, white or yellow low iron sphalerite, and minor iron sulfide. Silver averages ≤20 ppm, with arsenic values mostly <100 ppm but as high as 0.1 percent; gold is not anomalous. Mineralization is mainly strata bound within multiple calcareous horizons, including calcareous sandstones, breccias, and lacustrine limestones, with replacement, vein, and openspace fill styles with banded epithermal textures. Mineralization is thickest adjacent to a north-dipping fault that controls the southern margin of the basin. Vein mineralization occurs in Eocene marl and limestone adjacent to the fault which is interpreted as a feeder. Zinc-lead sulfide mineralization passes to celestite moving north and, thus, away from the fault.
The Sedjenane basin is controlled by a right-stepping jog in the crustal-scale Ghardimaou-Cap Serrat fault zone, which underwent late Neogene right-lateral transtension during extensional collapse of the Atlas orogen. The adjacent Oued Belif magmatic breccia complex is emplaced into a Triassic salt diapir in the extensional jog zone and hosts minor gold and copper mineralization. Volcanic and epiclastic rocks in the complex are intruded by late Miocene rhyodacitic flow domes and cut by diatreme breccias. Younger Pliocene alkalibasalts occur in the fault zone outside the complex.
The Bou Aouane deposit in northern Tunisia (#39, Figs. 1, 7) occurs on the northern margin of the Majerda basin, a major postcollisional pull-apart Neogene to Quaternary basin controlled by right-lateral movement on splays from the Ghardimaou-Cap Serrat fault system (Fig. 8). Mineralization is strongly fault controlled and similar to that at Sidi Driss and Oued Amizour deposits, comprising strata-bound replacement, vein and cavity-fill low iron sphalerite, minor galena, and trace pyrite. Silver contents are low (mostly <1 ppm), but arsenic values reach 0.1 to 0.5 percent in zinc-rich mineralization. Sulfides are hosted by late Miocene lacustrine limestones and carbonate-cemented sandstone and fanglomerate breccias. The Late Cretaceous carbonates in the footwall of the basin-controlling fault are cut by a set of north-northeast− trending zinc-lead mineralized veins that were the original target of the early miners. These veins opened along dilational fractures during right-lateral movement on the east-northeast−trending basin-bounding faults.
Similar vein-hosted mineralization is widespread elsewhere in the Late Cretaceous of northern Tunisia. Mineralization in Miocene basins is also common, although less well preserved due to uplift and erosion following Pliocene inversion.
The Neogene Atlas deposits, whether hosted by sedimentary or volcanic rocks show similar features, indicative of relatively shallow and low-temperature formation. The fact that deposits can occur with or without associated magmatic rocks and, in contrast to epithermal deposits, have little or no associated enrichment in gold, and mostly low-level arsenic and silver, suggests that mineralizing fluids are unlikely to have been predominantly of magmatic origin. Localization of deposits within a magmatic province related to postcollisional extensional collapse suggests that high-heat flow, magmatism, and faulting have all acted to focus flow of basinal brines from overthrust passive-margin basinal sequences into pull-apart Neogene basins, where mixing with fluids of magmatic origin may also have occurred.
The large and high-grade Angouran zinc-lead deposit (#40, Figs. 1, 7) is located in the Cimmerian Sanandaj-Sirjan zone of northeastern Iran. The deposit is currently exploited only for nonsulfide zinc mineralization based on a resource of 14.6 Mt at 22 percent Zn and 4.6 percent Pb. An additional sulfide resource of 4.7 Mt at 27.7 percent Zn, 2.4 percent Pb, and 110 g/t Ag remains unexploited. The sulfide mineralization occurs as one lens of massive sulfide in a metamorphic core complex, replacing a marble unit semiconcordantly to discordantly along a contact with underlying mica schist (Gilg et al., 2006). The core complex is dated as early Miocene, emplaced during orogenic collapse following Paleogene to Oligocene collision with Arabia and closure of the Neotethys Ocean. The core complex is unconformably overlain by a late Miocene volcanic and evaporite-bearing marine to continental sedimentary rock sequence.
The massive sulfide replacement mineralization is fine grained and postmetamorphic, containing breccia fragments of the host rocks. Sphalerite is iron poor, occurring with minor galena and pyrite in a gangue of anhydrite, quartz, muscovite, and dolomite. The mineralizing fluids were relatively low temperature (<200°C) saline brines (Gilg et al., 2006).
The sulfide mineralization grades upward into mixed sulfide-carbonate mineralization and then into a zinc carbonate deposit. Boni et al. (2007) interpreted the smithsonite ore to have formed in two stages, with an initial hypogene stage when smithsonite was precipitated with galena, pyrite, and arsenopyrite from low temperature-reduced, pH neutral, and CO2-rich fluids, and a later supergene stage.
Although the fluid chemistry may have been similar to an MVT system, the style of mineralization and metamorphic crystalline host rocks at Angouran are clearly quite different. However the tectonic and basinal setting shows strong similarities to the Atlas deposits, and the prevalence of fluids of MVT affinity suggests a significant input of basinal brines to the mineralizing system. Gilg et al. (2003) suggested that mineralization was broadly MVT and probably shared a similar Miocene age and structural control with the MVT deposits in Cretaceous rocks of central Iran, including Iran Kuh and Mehdi Abad. Gilg et al. (2006) suggested that the mineralization involved interaction of modified, strongly evaporated Miocene seawater with the exhumed metamorphic core complex and that contribution of metals from Miocene igneous rocks was possible. Boni et al. (2007) suggested that hypogene smithsonite was deposited during a waning stage of Cenozoic volcanic activity.
Himalayan fold belt and foreland
Lanping-Simao basin: The Jinding deposit (#44, Figs. 1, 8; Table 1) in western Yunnan is the largest zinc deposit in China. It occurs in the Lanping-Simao basin which accumulated marine and continental sediments from the Triassic to the Eocene, prior to uplift and deformation in the Himalayan orogeny. Many small zinc-lead occurrences are known in the basin (Watson et al. 1987), but Jinding is the only large orebody.
The Jinding deposit is comprised of three main zones, although multiple are interpreted as part of a larger original body cut by a series of faults (Xue et al., 2007). Sulfide mineralization comprises sphalerite, galena, and pyrite; silver content is low. Abundant celestite occurs as gangue with barite, calcite, quartz, anhydrite, and gypsum; bitumen also occurs with the ore. The oxidized zone (down to about 100 m) comprises a supergene assemblage of smithsonite, hydrozincite, cerussite, and strontianite.
Mineralization is hosted in a Paleocene alluvial fan sequence and carbonate breccia in the footwall of a major thrust. Most mineralization occurs in strata-bound zones in sandstone with limestone fragments where calcite cement has been replaced by sulfide and celestite. Underlying irregular mineralized zones occur in lacustrine evaporite-collapse breccias with limestone and sandstone blocks in a sandy to argillaceous matrix with carbonate. Mineralization occurs as openspace fill and replacements in breccia matrix, with local replacement of fragments producing massive sulfide. The breccias overlie gypsum- and celestite-bearing siltstone and sandy limestone. Limited mineralization also occurs in Triassic to Cretaceous sedimentary rocks above the thrust. Fluid inclusion data indicate low temperatures (110°–150°C), with salinities of 1.6–18.0 wt percent NaCl equiv, whereas lead isotope data suggest a predominantly nonradiogenic lead source, and sulfur isotope data are compatible with organic or bacterial reduction of evaporitic sulfate (Zhang et al., 2002; Xue et al., 2007).
The northwest-elongated Lanping-Simao basin straddles the boundary of the Indochina and Simao blocks in south-western China, bounded on the northeastern side by the Ailao Shan-Red River fault system. It evolved as a foreland basin to the Indosinian orogen and was probably contiguous with the southern part of the Songpan-Garze remnant ocean basin prior to major sinistral offset on the Ailao Shan-Red River fault and associated structures in the Neogene (Leloup et al., 1995). The Songpan-Garze basin contains up to 15 km of Triassic flysch that became progressively inverted and deformed in the Late Triassic and Jurassic, before being further deformed during Neogene Himalayan orogeny (Roger et al., 2010). In the Lanping-Simao basin, a thick Triassic marine sequence with local felsic volcanic rocks is overlain by Jurassic to Eocene paralic and continental sedimentary rocks, including thick playa-lake sequences with carbonates and evaporites, the host to mineralization at Jinding.
Basin development was controlled mostly by north-northwest− trending faults, with westward overthrust nappe structures possibly initiated during and after deposition of the host Yunlong Formation. Mineralization occurring both above and below the mine thrust suggests a mainly postthrusting age. Parallel thrust faults are unmineralized.
Movement on the Ailao Shan-Red River fault system was mostly early Miocene (Leloup et al., 1995), postdating basin deposition. Mineralization is younger than Paleocene and fission-track ages suggest an Oligocene age (Xue et al., 2007), accompanying Himalayan uplift and predating large-scale fault movement. Therefore, mineralizing fluids could have been derived from the larger Songpan-Garze sedimentary rock pile when the Lanping-Simao basin was still contiguous.
Kyle and Li (2002) proposed focused discharge of a metal-and petroleum-bearing brine sourced from a Mesozoic marine sequence at depth, with ore deposition occurring on mixing with shallow ground water containing bacterially reduced sulfur by replacement of calcite cement and limestone fragments. Mou et al. (2002) suggested that mineralizing fluids were related to local trachytic magmatism dated at 68 to 23 Ma. These trachytes form part of a suite of Paleogene alkaline magmatic rocks along the Jinshajiang zone that is associated with porphyry Cu-Au mineralization (Hou et al., 2007). On the basis of primitive Pb and noble gas isotopic composition, Xue et al. (2007) proposed that mantle-derived fluids were responsible for metal transport.
Although Jinding shows differences from typical MVT or sandstone-hosted deposits in setting, style, and controls, it does show similarities with other MVT deposits formed within some orogens, such as those in the Atlas belt and in Iran. These can be considered as subtypes of MVT deposits, and the unusual features can be related to the active tectonic foreland setting. The fluids that formed Jinding could be typical of MVT, and the simple chemistry does not suggest significant magmatic input. A metal-bearing basinal brine may have been derived by compressional loading of the Lanping-Simao basin and may have interacted with local highly saline evaporitic brines to precipitate the sulfide minerals. The Lanping-Simao basin is an offset segment of the huge Songpan-Garze Triassic flysch basin (Roger et al., 2010). The importance of basinal fluids is supported by the bitumen association.
Northern and western Himalayan foreland: The scale of the Himalayan orogen and orogenic foreland suggests substantial potential for additional deposits, but none is documented in the Mesozoic-Paleogene foreland basins on the southwestern margin of the Songpan-Garze basin (Fig. 8). This region of the northern Tibet plateau is remote, high-altitude, and poorly known.
The Wulagen deposit (#45, Figs.1, 8) in western Xinjiang province, western China, is in the foreland of the Kunlun fold belt in the western part of the Himalayan orogen. Sphalerite, galena, and pyrite mineralization occurs in Eocene terrigenous sandstone, conglomerate, and limestones, with early gypsum and a peripheral celestite deposit (Li et al., 2005). Lead isotope values are highly nonradiogenic and similar to Jinding. Mineralization has been linked to brine flow related to Himalayan orogeny (Liu et al., 2002).
The Kalangu deposit (Fig. 8) in the Kunlun foreland southeast of Wulagen has been described as a Pb-Zn-Co-Ni MVT deposit with breccia-hosted mineralization in Devonian-Carboniferous sandstone and limestone (He et al., 2000).
Kangdian district: The Kangdian district, straddling the Yunnan, Sichuan, and Guizhou provinces in southwest China, hosts a number of major zinc-lead deposits including Daliangzi, Tianbaoshan, and the deposits of the Huize subdistrict (#41–43, Fig. 1, 8). This is one of the most important zinc-lead districts in China with a 2,000-year mining history. Many of the deposits have been deeply oxidized following Neogene uplift and a substantial proportion of production has been from oxidized ore. Hypogene mineralogy includes sphalerite, galena, pyrite, and marcasite with minor chalcopyrite and arsenopyrite. Silver grades from 60 to 160 g/t are reported from the main deposits, and Cd, Ga, and Ge are also recovered at Huize (Han et al., 2007).
Mineralization is hosted primarily in Upper Sinian (late Neoproterozoic; Daliangzi and Tianbaoshan) and Early Carboniferous (Huize) carbonates, although some mineralization occurs in rocks as young as Jurassic. Deposits are located where favorable host units are cut by district-scale northwest-and northeast-trending faults. Mineralization occurs within faults and related breccia zones, as dissolution cavity fill and as more limited strata-bound replacement bodies (Zheng and Wang, 1991; Zhou et al., 2001; Huang et al., 2003; Han et al., 2007; Khin Zaw et al., 2007). Mineralization is typically sulfide rich with sphalerite, galena, and pyrite in carbonate gangue.
The Sinian deposits are hosted by evaporitic and algal platform dolomites of the Dengying Formation, deposited on a basement paleohigh and unconformably overlain by Cambrian black siltstone and mudstone (Zheng and Wang, 1991; Khin Zaw et al., 2007). Mineralization is structurally controlled, including open-space fill, breccia- and vein-hosted styles. Daliangzi is the largest deposit, located within a sinistral jog on a major northwest-trending fault zone. Tianbaoshan, 70 km to the northwest, has similar mineralogy and style.
The Kuangshanchang and Qilinchang deposits in the Huize subdistrict occur in Early Carboniferous dolostones of the Upper Baizuo Formation within a thick Devonian to Early Permian limestone-dominated sequence, located 80 km east of Daliangzi (Zhou et al., 2001; Han et al., 2007). Rare mineralization also occurs within nearby Late Permian altered ultramafic instrusions of the Emeishan flood basalt province (Han et al., 2007). Historic production from oxide and sulfide is ≥5 Mt of contained metal at grades averaging about 20 percent Zn + Pb. Mineralization at Kuangshanchang occurs as irregular pods and zones as much as 50 m wide within a steeply dipping northeast-trending fault zone and extends to depths of more than1 km. Oxidation extends to depths of as much as 500 m. Qilinchang is hosted by a subparallel northeast-trending fault zone 3 km to the east. Sphalerite, galena, pyrite, and very minor chalcopyrite occur as dissolution replacement and open-space fill with dolomite and calcite gangue (Huang et al., 2003). Sulfide minerals are typically coarse, with early crystalline iron-rich sphalerite and subordinate later iron-poor colloform sphalerite
Samarium-Nd dating of calcite from Huize suggests a Triassic age for ores in Carboniferous rocks, but with a large error range (Li et al., 2007), such that the age of mineralization is poorly constrained. Lead isotope data from Huize indicate a mixed upper-crustal and orogenic Pb source, and radiogenic Sr isotopes suggest basement involvement in the ore-forming process (Zhou et al., 2001; Han et al., 2007). Lead isotope data from the Daliangzi and Tianbaoshan deposits show a wide range (Zheng and Wang, 1991) and are not very meaningful. Sulfur isotope data from the deposits suggest an evaporitic sulfur source.
The deposits in the Kangdian region show a number of features that are not typical of MVT deposits, including the strong fault control, relatively high formation temperature (165°–220°C; Han et al., 2007) and high silver contents. Han et al. (2007) suggested a structurally controlled and deformed variant of MVT mineralization. The district has not been affected by magmatism since the mafic Emeishan event and magmatic input to the system is unlikely.
There is no direct control on the age of the Sinian carbonate-hosted deposits, but the similar chemical signature, mineralogy, style, and structural control suggests a common origin with the Carboniferous carbonate-hosted deposits within the district. Occurrence of mineralization in Jurassic carbonates suggests a maximum age.
The Kangdian district is located along a major regional northwest-striking fault trend in the northwestern part of the South China terrane, about 200 km of the Songpan-Garze flysch basin (Fig. 8). The Youjiang Triassic basin lies to the southwest. Both basins were inverted and closed in the Jurassic. Maximum uplift of the Songpan-Garze basin did not occur until Indian plate collision commenced in the Paleogene. The Himalayan orogeny resulted in regional uplift through southwest China and large-scale sinistral movement on regional northwest-trending faults as part of the extrusion of Southeast Asia (Tapponnier et al., 1982; Leloup et al., 1995).
Mineralization in the Kangdian district may be related to either event. The strong control by northwest faults and related antithetic east-northeast structures in dilational orientations may favor an origin during Indian collision in the Himalayan foreland.
Summary and Conclusions
The Tethyan belt hosts a range of significant zinc-lead deposits and districts which can be related to specific phases of orogeny. Due to diachronicity of tectonic events from east to west across the Tethyan belt, the various metallogenic stages do not fit into neat time slices. However, a number of important stages can be distinguished within the Neotethyan cycle and can provide indications of prospectivity of specific areas within the belt: (1) Late Paleozoic rift-sag phase SHMS and MVT mineralization in Cimmerian and northern Gondwana terranes; (2) Jurassic rift-sag phase SHMS and MVT mineralization on the southern Neotethys margin; (3) Cretaceous VHMS along the northern Neotethys margin in back-arc basins and in remnant Paleotethys basins; (4) Cenozoic CRD and skarn deposits in collisional arcs; and (5) Cenozoic MVT and hybrid MVT deposits in collisional orogens and orogenic forelands.
Whereas the known endowment of zinc-lead in the Neotethys region lies mainly within young Cenozoic orogenic deposits, some of the other deposit types have substantial upside potential for new discoveries. Much of the belt is poorly explored for a range of geographic and political reasons, and significant new discoveries are to be expected if the opportunities are created to support systematic modern exploration.
Globally, as well as within the Tethyan region, the Devonian to Carboniferous time window hosts a disproportionately large number of SHMS deposits (e.g., Red Dog, Alaska; Rammelsberg, Germany; the Qinling belt, China) that can be correlated with tectonic activity and phases of continental breakup and stratified ocean anoxia (Goodfellow and Lydon, 2007). At present, the Sopokomil deposit in Sumatra is the only known SHMS deposit associated with late Paleozoic Neotethyan rifting, although the Famennian-Tournaisian MVT districts of the Canning and Bonaparte basins can be related to a slightly older failed rift stage. Through India, Arabia, and Africa, these older basins are extensively covered in the absence of major uplift or deformation and are poorly preserved in parts of the Asian Cimmerian belt because of the intensity of subsequent collision and uplift. The known endowment indicates prospectivity of Late Paleozoic rift-sag basin remnants through the Gondwanan terranes that now comprise the belt west from central China through Iran and Turkey to Europe.
Known Mesozoic SHMS deposits are limited to the Jurassic Duddar deposit in Pakistan, Filizchai in Azerbaijan, and possibly Hakkari in Turkey. Duddar provides an indication of prospectivity of rift-sag basins of this age related to final Gondwana break-up on the southern Neotethys margin. Extension on the northern Neotethys margin also occurred in the Late Jurassic, following collapse of the Cimmerian orogen, and led to development of oceanic basins in back-arc settings from Iran to central Europe. The Jurassic Filizchai deposit in Azerbaijan is located in a Jurassic back-arc basin and is an indication of the potential of these extensional volcano-sedimentary sequences for large zinc-lead deposits.
The Cretaceous calc-alkaline arc-related magmatism in the Balkans and Turkey is associated with a very well endowed metallogeny. However, it is copper-gold dominated with important porphyry and epithermal copper-gold mineralization in the Banat (Romania), Timok (Serbia), and Srednogorie (Bulgaria) magmatic complexes (Heinrich and Neubauer, 2002; Lips, 2007). Only the Pontide belt in northeastern Turkey and Georgia, which is possibly related to back-arc extension, contains economically significant zinc-bearing VHMS mineralization.
The calc-alkaline magmatism in the Oligocene-Miocene related to postcollision subduction is a very significant tectonic event with respect to zinc-lead metallogeny, particularly in southern and southeastern. Economically, the most important deposits are CRD and skarns, typified by the Trepča (Serbia-Kosovo) and Kassandra (Greece) districts. Improved understanding of the geologic controls for this type of mineralization is being applied to ongoing exploration in these districts, and elsewhere in the region, and has resulted in new discovery and development. Epithermal zinc-lead mineralization related to this magmatic tectonic event is widespread throughout the region, but the deposits tend to be small and low grade.
Mesozoic and Cenozoic MVT mineralization is the most economically important style of zinc-lead mineralization in the Tethyan belt.
Some of the Neotethyan MVT districts are interpreted to have formed during basinal extension or inversion events, such as the Alpine deposits. Most are interpreted to represent fluid-flow systems within orogens or in foreland settings driven by compression or orgenic uplift, such as the Iranian, Atlas, Silesia and Cevennes districts. Although in some cases there is still significant disagreement as to timing of mineralization, the wide range of tectonic settings for MVT deposits is well illustrated in the Tethyan belt. Whereas the mineralizing processes in different settings involve similar epigenetic low-temperature systems, better understanding of the timing and controls of mineralization in specific districts will help target new discoveries.
The Tethyan belt also hosts a number of unusual hybrid zinc-lead deposits, including some of the largest such as Jinding (China) and Angouran (Iran). The deposits classified here as hybrid generally occur within areas of postorogenic extension, which in the case of the Atlas belt, Angouran, and Jinding regions was accompanied by minor alkaline or subalkaline magmatism. The Kangdian deposits, however, occur in an orogenic foreland with no associated magmatism. In some districts, evidence for classification is limited. For example, the Miocene volcanic rock-hosted Oued Amizour deposit (Atlas belt, Algeria) is considered as a hybrid deposit because of generally low precious metal content and iron-poor sphalerite, as well as the similarity to carbonate-hosted Miocene deposits in Tunisia. In contrast, the mineralization at La Union (Betic belt, Spain) is considered to be epithermal and related to the host Miocene volcanic rocks. Oued Amizour, Angouran, and Jinding may represent deposits formed in similar settings to that at the La Union deposits but where fluid systems were dominated by a basinal brine with limited magmatic input.
In view of their economic importance a better understanding of the hybrid type of mineralization would open up important new exploration opportunities within the Tethyan belt.
This paper covers zinc-lead districts with active mines, many of which are poorly described in the published literature. The authors acknowledge the numerous company geologists who enthusiastically introduced their mines and generously provided information that was recorded in our field notebooks. The conclusions drawn from these observations are those of the authors alone.
The authors are pleased to acknowledge the constructive comments by two Society of Economic Geologists reviewers, many of which have been incorporated into this text, and in particular, the supportive criticism provided by Richard Goldfarb.
Figures & Tables
The Challenge of Finding New Mineral Resources: Global Metallogeny, Innovative Exploration, and New Discoveries
VOLCANIC-ASSOCIATED and sedimentary-exhalative massive sulfide deposits on land account for more than one-half of the world's total past production and current reserves of zinc and lead, 7 percent of the copper, 18 percent of the silver, and a significant amount of gold and other by-product metals (Singer, 1995). A new source of these metals is now being considered for exploitation from deep-sea massive sulfide deposits. Because the oceans cover more than 70 percent of the Earth's surface, many expect the ocean floor to host a proportionately large number of these deposits. However, there have been few attempts to estimate the global mineral potential. Significant accumulations of metals from hydrothermal vents have been documented at some locations (e.g., 91.7 Mt of 2.06% Zn, 0.46% Cu, 58.5 g/t Co, 40.95 g/t Ag, and 0.51 g/t Au in the Atlantis II Deep of the Red Sea: Mustafa et al., 1984; Nawab, 1984; Guney et al., 1988). Even more metal is contained in deep-sea manganese nodules. Current estimates in the U.S. Geological Survey (USGS) mineral commodities summaries indicate a global resource of copper in deep-sea nodules of about 700 Mt. In the Pacific "high-grade" area, an estimated 34,000 Mt of nodules contain 7,500 Mt of Mn, 340 Mt of Ni, 265 Mt of Cu, and 78 Mt of Co (Morgan, 2000; Rona, 2003). A number of countries, including China, Japan, Korea, Russia, France, and Germany, are actively exploring this area.