Abstract Tectonic, geologic, geochemical, geochronologic, and ore deposit data from the U.S. Geological Survey-led assessment of 26 porphyry belts identified in the central Tethys region of Turkey, the Caucasus, Iran, western Pakistan, and southern Afghanistan relate porphyry mineralization to the tectonomagmatic evolution of the region and associated subduction and postsubduction processes. However, uplift, erosion, subsidence, and burial of porphyry systems, as well as post-mineral deformation, also played an essential role in shaping the observed metallogenic patterns. We present a methodology that systematically evaluates the relationship between the level of erosion, the extent of cover, and the number of known porphyry occurrences in porphyry belts. Porphyry belts that exhibit coeval volcanic-to-plutonic rock aerial ratios between 33 and 66 and limited cover contain numerous identified porphyry occurrences. These belts are relatively well explored because porphyry systems are not eroded or buried. Porphyry belts with volcanic-to-plutonic ratios that are greater than 66, but are modestly covered, contain fewer identified porphyry occurrences. Current exploration in these belts is increasingly identifying porphyry systems under associated epithermal deposits. Porphyry belts that show volcanic-to-plutonic ratios that are greater than 66, but are extensively covered, contain few identified porphyry occurrences. These belts have not been extensively explored but have potential for discoveries under cover. Deformed porphyry belts exhibit variable volcanic-to-plutonic ratios that are typically below 33, but can be as high as 60. Commonly, these deformed belts are extensively covered. Exploration efforts for porphyry deposits in these variably exhumed belts have been limited. Exploration has resulted in the identification of 62.7 million tonnes (Mt) of copper, 2.0 Mt of molybdenum, and 4.200 t of gold in the 45 porphyry deposits contained in the 26 porphyry belts of the region: (1) 54.7 Mt of copper (87% of total), 1.74 Mt of molybdenum (87%), and 3,370 t of gold (80%) occur in the 25 deposits of the four porphyry belts that exhibit coeval volcanic-to-plutonic ratios between 33 and 66 and limited cover; (2) 5.44 Mt of copper (9%), 0.148 Mt of molybdenum (7%), and 581 t of gold (14%) are contained in the 11 deposits of the 11 porphyry belts that display volcanic-to-plutonic ratios greater than 66 and modest cover; (3) 2.08 Mt of copper (3%), 0.110 Mt of molybdenum (6%), and 244 t of gold (6%) occur in the seven deposits of the three porphyry belts that have volcanic-to-plutonic ratios that are greater than 66 and extensive cover; and (4) 0.388 Mt of copper (1%), 0.006 Mt of molybdenum (<<1%), and 6 t of gold (<<1%) are contained in the two deposits of the eight deformed and covered porphyry belts with variable but typically low volcanic-to-plutonic ratios. The central Tethys region is receiving considerable exploration attention. It hosts the Kadjaran (4.6 Mt Cu), Sungun (5.1 Mt Cu), Sar Cheshmeh (8.9 Mt Cu), and Reko Diq (23.0 Mt Cu) world-class porphyry deposits. Continued exploration for porphyry deposits in the region will likely lead to new discoveries in known porphyry belts, particularly under cover and below high- and intermediate-sulfidation epithermal systems.

Full article available in PDF version.

Abstract T his F irst day of the field trip visits Proterozoic iron deposits at the Podunk and Skiff Mountain iron mines, in the eastern Adirondack Mountains of New York state. Included are roadcuts to see representative lithologies and structures in the region surrounding the iron deposits. The origin of these iron deposits has been controversial, but studies by Foose and McLelland (1995) and more recently by McLelland et al. (2001b , 2001c ) provide strong evidence for a high-temperture, intramagmatic origin related to late stages the Lyon Mountain Granite and correlative intrusions during the latter part of the 1090 to 1030 Ma Ottawan orogeny. The great majority of the deposits consist of low Ti magnetite ore accompanied by apatite and aegerine-augite. The apatite has high concentrations of rare-earth elements (REE) indicating to Foose and McLelland (1995) that the deposits are of Kiruna (REE-Au-U-Cu) type. This is further supported by persistent sodic (i.e., albitic) alteration associated with the ores. Most of the iron ores appear to be undeformed although they may occur in strained host rocks. Deposits are intimately associated with late tectonic to post-tectonic Lyon Mountain Granitic Gneiss that was emplaced at ca. 1055 Ma, during the waning stages of the ca. 1090 to 1030 Ma Ottawan Orogeny.

Abstract T his F irst day of the field trip visits Proterozoic iron deposits at the Podunk and Skiff Mountain iron mines, in the eastern Adirondack Mountains of New York state. Included are roadcuts to see representative lithologies and structures in the region surrounding the iron deposits. The origin of these iron deposits has been controversial, but studies by Foose and McLelland (1995) and more recently by McLelland et al. (2001b, 2001c) provide strong evidence for a high-temperture, intramagmatic origin related to late stages the Lyon Mountain Granite and correlative intrusions during the latter part of the 1090 to 1030 Ma Ottawan orogeny. The great majority of the deposits consist of low Ti magnetite ore accompanied by apatite and aegerine-augite. The apatite has high concentrations of rare-earth elements (REE) indicating to Foose and McLelland (1995) that the deposits are of Kiruna (REE-Au-U-Cu) type. This is further supported by persistent sodic (i.e., albitic) alteration associated with the ores. Most of the iron ores appear to be undeformed although they may occur in strained host rocks. Deposits are intimately associated with late tectonic to posttectonic Lyon Mountain Granitic Gneiss that was emplaced at ca. 1055 Ma, during the waning stages of the ca. 1090 to 1030 Ma Ottawan Orogeny.

Abstract Adirondack iron ores consist primarily of massive magnetite that generally occurs in layers or in elongated shoots parallel to fold axes. The magnetite is commonly accompanied by REE-enriched apatite and aegerine-augite. Hand lens inspection of ore reveals numerous octahedra indicating that the ore is either undeformed or recrystallized. The ore is invariably associated with various subunits of Lyon Mt. Granitic Gneiss (LMG), which are either in close proximity or serve as the host rock. A strong correlation exists between occurrences of ore and the presence of albitic subunits of LMG. Detailed investigations of these subunits demonstrate that they result from replacement of LMG microperthite by almost pure albite (˜Ab 98 ). The replacement process can be followed through initial stages of checkerboard albite and finally to quartz-albite rocks. Magnetite concentrations commonly occur in proximity to these rocks and almost every magnetite deposit hosted by granitoids shows evidence of checkerboard albite in the wall rocks. Thin section examination of several layered magnetite deposits demonstrate that they are intimately interleaved with highly deformed feldspathic wall rock that is grain size reduced and contains rolled feldspars reflecting shear strain. Present in the magnetite are crystals of bright green aegerine-augite interpreted to be coeval with the ore and undeformed even at their edges. This observation indicates that the magnetite is also postdeformational, an interpretation supported by narrow veinlets of magnetite that cut deformed feldspar tails at high angles but remain undeformed. It is proposed that ore constituents were transported through, and deposited within, fracture systems that localized iron-bearing fluids. An origin of this sort is consistent with either hydrothermal or immiscible magmatic processes. The latter possibility is considered to be unlikely, since the magnetite appears to be in equilibrium with the several silicate phases that it is in contact with. Moreover a hydrothermal origin is supported by the ubiquitous presence of checkerboard albite. Oxygen isotope studies indicate that the sodic, ore-bearing hydrothermal fluids equilibrated with wall rocks and ore at temperatures of 600°–700°C. The large scale of sodic alteration and magnetite deposition are best explained by a regional fluid of surface origin that evolved into saline brines either by evaporation or by interaction with evaporitic deposits. Such fluids are commonly associated with rare-earth-enriched, Kiruna-type, low Ti, Fe oxide deposits similar to those present in the Adirondacks.

Abstract T his D ay of the field trip visits the large Chateaugay open pit of the Lyon Mountain group of iron mines, in the northern Adirondack Mountains, following by visits to roadcuts in the Adirondack Lowlands to the west, in the vicinity of the Balmat zinc mine. The Chateaugay open pit has superb exposures of iron ore remaining on walls and in the entrances to stopes, which clearly establish the geologic and paragenetic relations of the magnetite ores and yield compelling evidence for their high-temperature, intramagmatic origin via hydrothermal fluids (McLelland et al., 2001b, 2001c). A wide variety of rock types ranging from leucogranite to mineralized skarns are present. In the afternoon this day features stops at five roadcuts between the town of Gouverneur, New York, and the Balmat zinc mine to the east. These roadcuts provide a good overview of the regional geologic setting of the Balmat deposit, including stratigraphy, structure, deformation, and metamorphism. Whereas the geochronology in the Adirondack Highlands to the east is well established (e.g., McLelland et al., 2001c), the Lowlands is underlain mostly by metasedimentary rocks hence its precise age range is difficult to determine. One constraint is provided by U-Pb zircon ages of 1284 ±7 Ma, 1236 ± 6 Ma, and 1230 ± 33 Ma for the Gouverneur, Fish Creek, and Hyde School alaskite bodies, respectively, that occur in the Lowlands (Grant et. al., 1986; McLelland and Chiarenzelli, 1990; McLelland et al., 1992). Although these alaskite bodies were interpreted by Carl and Van Diver (1975) to

Abstract T he U nderground tour will examine Proterozoic Zn sulfide deposits of the Balmat Zn mine, described by deLorraine and Dill (1982) and in this volume by deLorraine (2001). The evening preceding the tour will feature a talk on Balmat geology. This talk will involve a slide show presentation with maps, cross sections, and mine models made available for inspection. The latest structural interpretations will be reviewed and there will be in-depth discussions regarding the response of massive sulfides to high-grade, near granulite- facies metamorphism in a sequence of interlayered silicated dolomitic marbles and pure marble units of extremely high ductility contrast. We will demonstrate that ore was tectonically remobilized 600 m and more laterally, by over 2000 m in the down-plunge dimension. This happened in several parent-daughter pairs. The degree and extent of remobilization of massive sulfide at Balmat appears to be unique anywhere in the world.

Abstract Zinc orebodies of the Balmat-Edwards-Pierrepont Zinc mining district in the northwest Adirondacks of New York State rank as near world-class deposits having nearly 40.8 million metric tonnes (Mt) of past production plus reserves grading 9.4% Zn. Orebodies occur in Mesoproterozoic siliceous dolomitic marble that was metamorphosed and polydeformed during the Grenvillian orogeny about 1.1 Ga. Remobilization of inferred syngenetic massive ore during high-grade metamorphism has been locally extensive depending on the stratigraphic unit from which a particular orebody originated. Two remobilized orebodies, the Loomis and Lower Gleason at No. 3 Mine, show clear linkage to the Upper Gleason, a massive, high-grade parent lens of ore. The extent to which ore was remobilized from the Upper Gleason has only recently been discovered. External remobilization is over 500 m laterally discordant to stratigraphy and over 2000 m in the down-plunge dimension. Daughter orebodies or remobilized daughter ore zones within orebodies are well documented elsewhere at Balmat. There also exist clearly discordant, externally remobilized, daughter ore-bodies for which the source or parent bed can be inferred but which have not yet been located. The Upper Fowler and Mud Pond orebodies are two such “orphans” whose existence depends upon a third, parent orebody hitherto unsuspected but now predicted to reside in unit 6. The extent to which ore is dissipated to tectonic slides is limited by the presence of thick, bedded anhydrite layers in the section. Tectonic slides die out in anhydrite so that sulfide migration is constrained by the impingement of faults into those strata. In the Fowler orebody, distances of remobilization less than several hundred meters are observed because the structure was encased by flowage of anhydrite very early on in its evolution, effectively sealing off any further sulfide migration. Plastic flow, and to some extent fluid-aided plastic flow, along ductile-brittle synmetamorphic faults or tectonic slides is thought to have been the dominant transport mechanism. There is a clear association between rock type and ore thickness. Ore is thicker where it follows the trends formed by the intersection of competent, silicated units with mineralized fault or tectonic slide surfaces, and thinner where following intersection trends of ductile rocks with fault surfaces. Substantial revisions are made here to the number of ore-forming cycles in the Balmat section from six or more, down to three. Evaporite deposition in the form of anhydrite is tied closely to sulfide deposition so that three “evaporite-ore” events are recognized in the Balmat section corresponding to source horizons in units 6, 11, and 14. Any ore in contact with other units in the Balmat section is “in transit” and may have been remobilized significant distances from its source bed.

Abstract T his P ortion of the field trip features visits to the worldfamous Sterling Hill and Franklin mines, in northwestern New Jersey, and their respective mining museums. Although both mines are no longer in operation, important geologic features can still be observed. At the Sterling Hill mine, we will have the opportunity to see zinc ore in place, both in an underground drift and in the Passaic open pit; at Franklin the pit is filled with water and only disseminated mineralization is still visible. The Furnace magnetite bed will also be seen adjacent to the Franklin open pit, as well as a large postore minette dike. If time permits we will visit a surface exposure of the Zero Fault in Franklin, which is an important regional structure that cuts the Sterling Hill orebody.

Abstract The New Jersey Highlands are underlain principally by Mesoproterozoic rocks that were metamorphosed at upper amphibolite to granulite facies between 1080 and1030 Ma during the Ottowan Orogeny. The oldest rocks are inferred to be metamorphosed ca. 1300 Ma dacite, tonalite, and trondhjemite and associated charnockitic plutonic and metavolcanic rocks of the Losee Metamorphic Suite. These originated in a continental margin magmatic arc setting dominated by calc-alkaline and tholeiitic magmatism. Rocks of the Losee record a compressional event in the north-central Appalachians that was likely coeval with the 1300 to 1200 Ma Elzevirian orogeny in the northern Appalachians and Grenville Province. The Losee is unconformably overlain by a sequence of supracrustal rocks older than 1100 Ma that were deposited in an extensional tectonic setting. These include quartzofeldspathic gneisses, metaquartzite, calc-silicate rocks, marble, and amphibolite. The earliest recognized part of this succession consists of metamorphosed arkosic and quartzose sandstones that were deposited in a continental rift basin. These are spatially associated with a bimodal assemblage of metarhyolite and metabasalt. Overlying sanddominated clastic rocks (quartzofeldspathic and siliceous calc-silicate gneisses) and marble are interpreted as a platformal, shallow-marine succession based on lithologic associations, stromatolite occurrences in marble, and stable isotope data. This succession grades into overlying supracrustal rocks that reflect an arc-derived sediment source, and that contain a higher proportion of mafic volcanic rocks, including locally pillowed metabasalts of MORB affinity. Losee and supracrustal rocks were intruded by voluminous, widespread synorogenic A-type granitoids of the Vernon Supersuite that consist of the 1116 ± 41 Ma hastingsite and biotite-bearing Byram Intrusive Suite and the 1095 ± 9 Ma hedenbergite-bearing Lake Hopatcong Intrusive Suite. The postorogenic 1020 ± 4 Ma Mount Eve Granite and associated 1004 ± 3 Ma pegmatites, which straddle the boundary between New Jersey and New York, provide a minimum age for the Ottawan orogeny in the Highlands. Discordant postorogenic pegmatites were emplaced at 998 to 989 Ma and 965 Ma. Mesoproterozoic rocks of the Highlands host economic deposits of iron, zinc, and graphite. Deposits of high Ti and low Ti magnetite ± hematite are widely distributed throughout the region and occur within virtually every Mesoproterozoic rock type. Small U and REE deposits are associated with a few of the Fe deposits. Neoproterozoic greenschist-facies felsic volcanic and terrestrial sedimentary rift basin rocks host small hematite deposits that have characteristics of iron-formation. Two large marble-hosted zinc (zincite, willemite, franklinite) deposits occur in the northwestern Highlands at Franklin and Sterling Hill, and marble-hosted sphalerite occurs at the Raub mine in the southwest Highlands. Zinc deposits at the Franklin and Raub mines directly overlie Mn-bearing Fe oxide deposits, implying a genetic relationship. Graphite deposits are confined to the eastern Highlands where they are hosted by sulfidic biotite-quartz-feldspar gneiss and metaquartzite. Available geologic evidence suggests that metals in the Zn and most of the Mesoproterozoic Fe deposits were introduced prior to ca. 1080 to 1030 Ma granulite facies metamorphism.

Abstract Structural and textural evidence within the Mesoproterozoic Sterling Hill Zn-Fe-Mn orebody suggests that it is a metamorphosed stratiform deposit, part of a subducting assemblage that was folded and subjected to sufficiently high pressure and temperature conditions to induce viscous or pseudoviscous flow in the carbonate host rock. This resulted in a high-density ore deposit sinking as an inverted diapir through the enclosing marble. During Phanerozoic time a possibly large part of the orebody was lost due to major faulting. The occurrence of an extensive rubble breccia body in the mine is evidence that a probable Cambro-Ordovician kars-tification event extended down into underlying Proterozoic rocks. Most recently saprolites, as much as 240 m deep, developed within the marble/amphibolite core of the orebody and also in rocks above in the hanging wall.

Abstract T he P urpose of this chapter is to review two aspects of the geochemistry of the Sterling Hill and Franklin zinc-ironmanganese deposits and the Furnace magnetite bed that underlies the Franklin deposit. These are (1) oxidation and sulfidation states determined from heterogeneous phase equilibria, and (2) stable isotopic compositions determined from analyses of carbonate, silicate, oxide, and sulfide minerals. The data place constraints on the genesis of the ores, which is the topic of the final section of the chapter. This review draws heavily from the results of my own dissertation research on Sterling Hill (Johnson, 1990; Johnson et al., 1990a) and from recent and continuing projects (Johnson et al., 1990b, Johnson, 1994, 1996, 1997; Volkert et al., 2000); it also includes the sulfur isotope results obtained by Ault (1957). For a complete review of the geology of the deposits, the reader is referred to the chapter by Metsger (2001), and to Metsger et al. (1958) and Frondel and Baum (1974). A complete catalog of the extensive literature on the deposits is given by Dunn (1995). The Sterling Hill and Franklin deposits are located in northwestern New Jersey within the Reading Prong-Hudson Highlands terrane, which is a belt of Mesoproterozoic sedimentary and igneous rocks that was regionally metamorphosed during the Grenvillian orogeny at about 1.0 Ga. Although the question has arisen as to whether the zinc and associated metals in these deposits were emplaced before or after the metamorphic event, it is now clear from structural, geochronologic, and phase equilibrium studies

Abstract F ew of the nearly 400 iron mines in the New Jersey Highlands share the historical significance of the Andover mine that assumed an important role during the American Revolutionary War. In 1778, possession of both the mine and the Andover furnace were taken by the Continental Congress to supply American troops with iron and steel (Bayley, 1910). The Sulfur Hill mine did not open until between 1855 and 1860 and thus played no part in this conflict. Individual production figures for these two mines are lacking for all but a few years; however, the combined total production is estimated at about 363,000 metric tonnes of ore (Bayley, 1910). The mines at Andover and Sulfur Hill are unique among the Highlands iron mines in affording an opportunity to examine two entirely different genetic types of iron mineralization. These deposits share few similarities beyond their close spatial association (ca. 200 m apart) and the fact that both deposits are shallow, having been worked mainly from open cuts .26 m deep and underground to a limited extent. Some of the principal differences between the two deposits include: (1) a Neoproterozoic age for ore and host rocks at Andover vs. a Mesoproterozoic age (pre- to syn- Ottawan orogeny) for ore and host rocks at Sulfur Hill; (2) mainly hematite ore at Andover vs. magnetite only at Sulfur Hill; (3) separate, discontinuous deposits having different geometries; (4) low-grade metamorphism of ore at Andover vs. high-grade (?) at Sulfur Hill; (5) higher iron content of ore

Abstract The Losee Metamorphic Suite, granites of the Vernon Supersuite, amphibolites, the Franklin Marble, and the Chestnut Hill Formation each contain magnetite or hematite deposits that were mined in the New Jersey Highlands during the last half of the 20th century and the first half of the 21st century. How-ever, not all of these Proterozoic magnetite deposits are the same. Grenvillian Losee-hosted magnetite de-posits occur as concordant veins and disseminations that precipitated from fluids released during the prograde granulite-facies breakdown of biotite, coeval with subduction of its dacitic arc protolith. The Vernon Supersuite-hosted magnetite deposits are chemically and structurally similar to the Losee de-posits and precipitated in a similar deep crustal environment during early or pre-Ottawan orogenic intrusive activity at ca. 1100 Ma. The Vernon Supersuite deposits may have precipitated out of late-mag-matic or deuteric iron-rich fluids that were generated during the local conversion of granite to iron-depleted alaskite. Although magnetite in most of the granite- and gneiss-hosted deposits contains 1 to 3 wt% TiO2, magnetite in some Grenvillian amphibolite-hosted deposits has up to 10 wt % TiO 2 , consistent with the higher temperature magmatic history of their basaltic protolith. The TiO 2 content of magnetite in the Grenvillian carbonate-hosted deposits is less than 0.2 wt % with high MnO contents consistent with distal volcanogenic marine deposition. Chestnut Hill-hosted deposits share some of the char-acteristics of banded iron formation.

Abstract The Purpose of this trip is to examine relations of the economic geology and mining history of the Vermont copper belt to the environmental behavior of these deposits and their potential future reclamation. In contrast, the 1993 Society of Economic Geologists field trip focused on the regional and economic geology of the copper belt (Slack etal., 1993). The Vermont copper belt, like many other mining districts, has had a long and colorful history (Abbott, 1973). This history spans the period of active mining from the discovery of the Elizabeth deposit in 1793 through its closure in 1958, to the present, as plans to reclaim the site are being made. Like other districts, the history is intimately intertwined with the economic development and early settlement of the region. Production was dominated by three main mines: Elizabeth, near South Strafford; Ely, near West Fairlee; and Pike Hill, near Corinth. In addition, several other smaller mines and prospects are found in the belt. All mines exploited copper-rich massive sulfide deposits, or their weathered equivalents. The earliest mining from Elizabeth was for iron from the gossan zone, followed by mining of pyrrhotite for the manufacture of copperas (hydrated ferrous sulfate). Copperas was produced by roasting the ores to oxidize the pyrrhotite. Resulting ferrous sulfate was leached from the roast beds with water, and concentrated in evaporating vats. During the late 18th and early 19th centuries, copperas was used for curing and setting colors in hides and pelts, and for making dyes, treating timbers and