Abstract The Horseshoe quarry is located in the SW¼, NW¼, NE¼, Sec.36, T.9S., R.7E., Saline County; Rudement and Equality 7½-minute QuadrangleIllinois (Figs. 1, 2). From Equality, travel south 2.0 mi (3.2 km) via county road to the foot of Wildcat Hills, then west 2.5 mi (4 km) on gravel road to a point 0.2 mi (0.3 km) past the turnoff to Glen O. JonesLake. The longabandoned quarry is in low, wooded hills immediately north of the road, on land administeredby the U.S. Forest Service.

Many structural domes and anticlines rise from undeformed surroundings; the general crust of the earth is neither shortened nor extended by these local swells or blisters, but the area of the plate upfolded is increased. With plastic material the increase is effected largely by flow; with brittle material, largely by fracture. Many mining districts are associated with upfolds of this type. Districts here described fall into two categories: (1) those whose structural frame is a dome, and (2) those whose structural frame is an anticline. Domes may show fractures which radiate from the apex, or concentric fractures which are segments of circles, of varying diameters but with a common center, the apex of the dome. Both types may appear on the same dome; the fractures of each type aid enlargement of the plate during doming. Sunlight and Kirwin, Wyoming, are minor districts with dominant radial fracture patterns. Vein matter was deposited while the walls of the vein fractures were being pulled apart. With a radial vein system the only way in which all the vein walls could be simultaneously pulled apart is by stretching of the fabric of an expanding dome. The structural setting of the Ophir, Utah, lead-silver district, and of the Matehuala, Mexico, copper district is that of a half dome truncated by a normal fault with downthrow away from the domical apex. Displacement on the fault is greatest opposite the apex and decreases progressively in both directions, becoming zero at the spring line. No part of the dome ever existed on the down-thrown side of the fault, which was a fracture before doming. Maximum uplift was centered on one side of the fault and there produced the half dome; but the pre-existing fracture offered locally an easier mode of uplift by rise of the foot-wall block. At Ophir ore shoots followed intersections on the half dome of radial fractures with limestone beds. At Matehuala stretching during doming was effected largely by flow of limestone, but a monzonite stock intruded in the half dome was too brittle to flow. The limestone pulled away from the unyielding stock; fractures concentrated around the periphery of the stock localized the Dolores copper ore bodies. In the Silverton-Telluride district, Colorado, fractures radiate from a relatively large, roughly circular graben, along whose margin monzonitic stocks were intruded. Evidence suggests that this fracture pattern resulted from domical uplift, with the graben at the apex. Transfer of volcanic material from depth to the surface in the central area produced a sag which has eliminated the upward bulge of the dome. Mineralization advanced outward from the graben step by step with the outward growth of the radial fractures. Copper-silver pipes within the fault zone bounding the graben were formed first, followed successively outward by base-metal deposits as veins, which were reopened to admit gold and silver, and by precious-metal vein deposits in the outermost zone. The structural setting of La Plata, Colorado, is that of a dome, truncated, south of its apex, by a zone of high-angle faults striking eastward. Displacements on the faults are greatest opposite the domical apex. The doming is accentuated by a horseshoe-shaped hinge fold, open on the south. Along the fold dips of the strata steepen sharply; outside it, dips are gentle, whereas inside it, they are nearly flat. Several stocks were intruded along the fold, and others inside it. The steep flexural fold and abundant intrusions suggest upward shove of a flat-topped piston, perhaps a magma column congealed in its upper part, but fluid and under pressure below. Fractures are abundant along the horseshoe fold, and, with respect to the dome, fall into two classes, radial and concentric. Gold-silver deposits were concentrated chiefly within or near the horseshoe fold, and in the eastward-trending fault zone. Doming, which began during the intrusive epoch, persisted through the period of metallization, because at that time older fractures were reopened, new radial and concentric fractures were created, and fractures of both generations became loci for ore bodies. The structure at Rico, Colorado, is that of a dome with eastern elongation. Superimposed upon the major dome, toward its eastern end, is a doubly plunging anticline, also with easterly trend, cut by fractures which parallel its axis, and by fractures normal to the axis. Rich ore bodies were localized at a stratigraphic horizon originally occupied by a bed of gypsum which was dissolved, leaving silty material which the ores replaced. Ribbon-shaped mantos lay directly above fractures, both of the longitudinal and transverse sets. Ore solutions ascended these fractures to form the mantos during late stages of the doming. The Goldfield, Nevada, district lies on the southwest flank of a dome encircled by a belt of intense alteration, and of complex fracturing, which probably coalesces at depth into one or more persistent faults concentric with respect to the domical apex, and which formed the channel for altering and metallizing solutions. The volcanic rocks were brittle when first fractured by doming, but solutions rising along the fractures of the circular belt softened the rock by alunitization and kaolinization. Silica-bearing solutions then created the irregular silica “ledges” at horizons close to the then surface. The soft rock encasing the ledges flowed, as doming persisted, but the brittle ledges fractured. Ledges which had no “keel” below them were inaccessible to gold-bearing solutions; those with keels extending down to the main ore channel received the rich ore bodies. Many mining districts are associated with doubly plunging anticlines, which with brittle rock are broken by fractures which strike parallel or normal to the axis. At Creede, Colorado, older extrusive rocks were flexed into a north-trending anticline. Younger extrusive rocks do not share in the folding, but faults which strike parallel to the anticlinal axis and dip toward it cut and displace both older and younger rocks; they form a graben along the crest of the buried anticline. These faults originated as tension fissures, the result of arching of the older volcanic rocks. After extrusion of the younger volcanic rocks, renewed uplift was concentrated along the abutments of the arch, in the footwalls of the graben faults. These faults were propagated upward through the younger volcanic rocks. The eastern graben fault, the Amethyst, fingers out at its southern end. Most of the silver ore of the district came from the southern segment of the Amethyst vein. Here intense local uplift in the footwall, unable to utilize the split-up fault as a lubricated plane of movement, tore apart the walls to permit entry of the silver-bearing solutions. The structure at Bodie, California, is that of an irregular anticline upon which are superimposed several domes. The country rock is volcanic. Most of the faults and veins strike parallel to the anticlinal axis and dip toward it; but the Fortuna fracture, which carried the richest ore body, lies in anomolous relation to the anticline, for it is neither a longitudinal nor a cross fracture. It seems to have resulted from an earlier deformation, but to have been utilized by the uplift which formed the anticline in such a way that its flat segment gaped open to admit rich silver- and gold-bearing solutions. Guanajuato, Mexico, lies on the northeast flank of a major anticline which plunges southeast. The anticline carries a crestal graben. The graben fault on the northeast flank is the Veta Madre, with maximum displacement on the northwest; displacement decreases progressively southeastward, in the direction of plunge of the anticline. Like the Amethyst fault at Creede, the Veta Madre originated as a tension fissure, but became an antithetic fault when the arch broke into segments under continued uplift. Major silver-ore bodies on the Veta Madre were localized where differential movement of the walls brought shallow cups in the footwall surface opposite planar areas in the hanging-wall surface. At El Oro, Mexico, the attitudes of remnants of an andesite flow overlying shale, together with the fracture pattern, indicate deformation to form a broad anticline trending north-northwestward. The San Rafael vein lies along a normal fault striking parallel to the anticlinal axis, with downthrow on the west, toward the axis. Faulting had been completed by the time of mineralization. Early, low-grade vein matter welded the fault, but arching continued and with it an urge toward resumption of faulting, prevented by the welding. The resulting strong shearing strain produced a number of vertical feather-joint branches in the hanging wall of the fault. These were mineralized by solutions rich in gold and silver. The Mogollon, New Mexico, district lies on the west flank of a large anticline trending and plunging north-northeastward. The Pacific-Great Western and Queen faults strike parallel to the anticlinal axis and dip eastward toward the axial plane. The block between these faults contains a local bulge truncated on the east by the Queen fault. Displacement on the fault is greatest opposite the crest of the bulge and decreases progressively in either direction. The local uplift in the footwall increased the displacement on the Queen fault, but it took place in the hanging wall of the Pacific-Great Western fault. The original displacement was reversed in the segment affected by the bulge. The bulge has the form of a doubly plunging anticline trending northward, parallel to the Queen and Pacific-Great Western faults. The chief productive veins of the district occupy cross fractures normal to the anticlinal axis. Most of those north of the highest point on the up-bowed axis dip southward, whereas most of those south of that point dip northward. These fractures gaped open, under continued bulging, in time to receive the richest surge of silver-gold solutions. The following generalizations appear valid. Uplift in these districts was accompanied by development of tension fissures. Uplift and consequent stretching of the arching plate persisted through the period of mineralization, but by this time stretching in many areas had reached a stage at which Assuring could no longer facilitate it; Assuring was succeeded by graben and antithetic faulting. Ore deposition sometimes preceded this faulting but more often followed it. The fracture pattern on these domes and anticlines developed as uplift progressed. Solutions deposited vein matter in those fractures which were permeable at the time and accessible from the main solution channel. Mesothermal deposits associated with domes and anticlines fall into groups defined by age of mineralization and by metallographic provinces, but epithermal deposits are scattered from one end of the Cordilleran region to the other. They show, however, a preference for major uplifts. Silverton, Rico, La Plata, and Creede lie on a tectonic element marked by recurrent uplift from the close of the Paleozoic to the Pleistocene. Epithermal deposits in Mexico are concentrated on the site of the persistently positive Occidental geanticline. The crystalline basement lies deep throughout much of Nevada, but Goldfield, Tonopah, and other epithermal districts lie above or close to relative highs in the basement which are much larger than the local uplifts with which these districts are associated. These major uplifts were developing while epithermal metallization was taking place. The whole Cordilleran region was fast assuming its present shape. The local phenomena of uplift, Assuring, intrusion, and metallization were satellitic features superimposed on the uplift of the Cordilleran region as a whole. Because of this fact, a deep-seated origin for epithermal ores is suggested.

Abstract A simplified geologic map of the North Island is shown in Figure 1. The oldest rocks which form the basement are of late Paleozoic to Mesozoic age. The New Zealand lithosphere only began to develop as a separate crustal entity in the late Cretaceous-early Tertiary when it broke away from the Gondwana supercontinent as the Tasman Sea opened (Sporli, 1987). Much of the geology of this continental fragment, which extends from New Caledonia to the Campbell Plateau, is obscured by the fact that about 70% of it is submerged (Fig. 2). New Zealand's Cenozoic history relates to its proximity to a major active boundary between the Indian and Pacific plates (Figs. 3 and 4). Accurate reconstruction of the plate boundaries for most of this era is difficult, although several versions are published (e.g. Cole and Lewis, 1981; Ballance et al., 1982; Brothers, 1984; Walcott, 1987). In the following summary, we focus on the products of arc magmatism and closely related hydrothermal activity (Fig. 5). We start with the present situation. The TVZ is a complex volcano-tectonic depression, filled with pyroclastic deposits and lavas, that is related to the westward dipping subduction zone of the Hik:urangi Trough (Fig. 6). It extends offshore into the Tonga-Kermadec arc and marks the start of the Pacific 'horseshoe of fire'. Convergence along the Hikurangi Trough is increasingly oblique southward to form a transform plate boundary as delineated by the Alpine Fault in the South Island (Figs. 2 and 3). The Benioff zone dips at a very shallow angle west of the Hikurangi Trough but becomes steeper westward to where it lies at about 80 km depth beneath the TVZ (Fig. 6). An accretionary prism, comprising Tertiary and younger sediments, lies above the shallower Benioff zone. Bounding the accretionary prism to the west are the Axial Ranges which are made up of Mesozoic greywackes and argillites of the Torlesse terrane; the North Island Shear Belt comprises a set of dextral north-trending faults that cuts across them (Fig. 7). The TVZ lies adjacent to the Axial Ranges, about 250 km west of the Hikurangi Trough, and extends from White Island to Tongariro. Its margins are defined by steep gravity gradients and distribution of volcanic vents, except to the northwest where it merges with the Coromandel Volcanic Zone (Rogan, 1982; Wilson et al., 1984). Northeast trending normal faults dominate the structural fabric, forming a series

Fossils and rock samples were collected from the Snowy Range Formation at 24 sections measured in the Horseshoe Hills and Bridger Mountains of Montana and eight sections in the vicinity of Yellowstone National Park in Montana and Wyoming. Where the Snowy Range Formation is overlain by the Maywood unit (Devonian), both were measured and sampled, although the Maywood proved to be unfossiliferous. Lowermost of the three members of the Snowy Range is the Dry Creek Shale which lies conformably on the Pilgrim Limestone. It consists of about 50 feet of purplish, thin-bedded, fissile to slightly plastic shale with a few irregular beds of brownish-gray, platy, dolomitic siltstone in the lower three fourths, and some thin beds of silty limestone or limestone-pebble conglomerate in the upper quarter. No evidence is present in this area for subaerial erosion between the Pilgrim and Snowy Range Formations, although beds of siltstone in the Dry Creek may reflect uplift and erosion at the source of terrigenous sediments. The middle member is the Sage, which averages about 200 feet thick where complete. Its base is marked at most localities by a 1-20-foot bioherm of columnar algal limestone; the remainder is a fairly regular alternation of 1–2-foot beds of limestone or limestone-pebble conglomerate with 2–4-foot beds of green shale or very argillaceous greenish-gray limestone. The upper part contains beds of noncolumnar algal limestone. This member was deposited far from shore in shallow turbid water that contained abundant calcium in solution. Microcrystalline calcite ooze, along with fine fragments of fossils and pellets, collected in ripple troughs and other depressions in the mud of the sea floor. These small accumulations became sufficiently consolidated to maintain coherence when excavated by currents that swept away clay particles and concentrated the limestone “pods” into beds that later were cemented to form limestone-pebble conglomerate. The uppermost member, the Grove Creek, is nowhere complete in this area; the upper part was removed by erosion at some localities and by faulting at others. The member consists of about 25 feet of dolomitized limestone-pebble or cobble conglomerate with intercalated beds of dolomitized, gray, splintery shale. This member owes much of its distinctive character to weathering that took place before deposition of the Upper Ordovician Bighorn Formation. The Maywood unit is a Devonian soil or weathered zone that overlies some part of the Snowy Range Formation in the northwestern part of the area of study but overlies formations as low as those in the Precambrian Belt Series or as high as the Upper Ordovician Bighorn Formation in other parts of Montana. It consists of a greatly varying thickness (averaging about 55 feet) of reddish-orange or brown, thin-bedded, silty dolomite or dolomitic limestone. At a few localities it is coarse-grained, thick-bedded, light-brown dolomite. No fossils were found in the Maywood of the area studied, but Devonian fossils have been collected from it in other parts of Montana. Fossils described are 80 species assigned to 48 genera of trilobites, 20 species assigned to 14 genera of brachiopods, four species in four genera of gastropods, two species in one genus of conodonts, one species of sponge, one of graptolite, two form species of algal limestone, and problematica . New taxa are the trilobites Comanchia lippa n.sp., Geragnostus ? insolitus n.sp., Monocheilus demissus n.sp., Pinctus ? artus n.sp., P. ? pullus n.sp., Pseudagnostus sentosus n.sp., Rasettia snowyensis n.sp., Saratogia carita n.sp., S. fracida n.sp., and Taenicephalus gallupensis n.sp.; the brachiopods Angulotreta catheta n.sp., A. glabra n.sp., A. vescula n.sp., Eoorthis remnicha var. A. n. var. and Huenella texana var. fortis n.var. Fossil species in the Snowy Range Formation are assigned to local zones that are based on ranges of genera and species of trilobites and which can be correlated with standard zones of the Cambrian Correlation Chart or with local zones of other areas. A few species from scattered localities near the base of the formation belong to the Aphelaspis or Dunderbergia zones of the Dresbachian Stage. Most species belong to zones in the Franconian. Lower-most of these is the Elvinia Zone (with Camaraspis Subzone and Irvingella major Zonule in the upper part) which corresponds to the Elvinia Zone of the Cambrian Correlation Chart. Next higher is the Taenicephalus Zone (with Parabolinoides Subzone at base) which correlates with the Conaspis Zone of the Chart. Above this is the Idahoia Zone (with basal I. wyomingensis Subzone, middle I. wisconsensis Subzone, and upper I. serapio Subzone) which correlates with the Ptychaspis Subzone of the Ptychaspis-Prosaukia Zone of the Chart. The uppermost zone of the Franconian is the Prosaukia Zone, which is equivalent to the Prosaukia Subzone of the Chart. Species of the Trempealeauan Stage are assigned to the Illaenurus Zone which corresponds to the Lower Trempealeauan of Texas or the lower part of the Saukia Zone of the upper Mississippi Valley. An alternative zonation is offered, based on the ranges of genera and species of brachiopods. Boundaries of most brachiopod zones fall near the levels of the boundaries of trilobite zones, but some do not. The Apsotreta expansa Zone belongs to the Dresbachian Stage. The Linnarssonella Zone and the Angulotreta tetonensis Zone (with Ceratreta-Eoorthis Subzone at base) correspond respectively to the Elvinia and Taenicephalus Zones of the lower part of the Franconian Stage. The Angulotreta vescula Zone corresponds to all but the uppermost part of the Idahoia Zone, and the A. catheta Zone (with Finkelnburgia osceola Subzone at top) is equivalent to this uppermost part of the Idahoia Zone and the entire Prosaukia Zone of the Franconian Stage as well as the entire Illaenurus Zone of the Trempealeauan Stage. No Franconian-Trempealeauan boundary is apparent in the brachiopod zonation.

Abstract The Felbertal scheelite deposit is located in the northern part of the central Hohe Tauern (Austria). It occurs in an up to 400-m-thick section of the Precambrian (?) to Cambrian Habach Group, consisting of fine- and coarse-grained amphibolites, hornblendites, I-type granites, and quartzites. In the present paper, a comprehensive review of the voluminous literature covering the geologic, mineralogical, petrographic, geochemical, microthermometric, tectonic, geochronological, and isotopic aspects of the deposit is given, and then an attempt is made to combine these various aspects into a unifying evolutionary model of ore genesis. The premineralization history of both ore fields of the Felbertal scheelite deposit starts with fine-grained amphibolites, classified as volcanic arc basalts, at 547 ± 21 Ma. Sills of hydrothermally altered pyroxenites and gabbros, followed by I-type granites, intruded the basalts during Cambrian time. This rock suite may have been derived by differentiation and fractional crystallization of a calc-alkaline basaltic magma in an active continental margin setting. Primary scheelite formation is linked to the subsequent emplacement of highly differentiated granitic rocks (with within-plate granite characteristics) some 515 m.y. ago, as indicated in the eastern ore field by a granite gneiss (522 ± 11 Ma) underlying a scheelite-rich quartzite (507 ± 29 Ma.). This elongate quartzite lens, the contiguous granite gneiss lens, and an underlying stockwork zone mark a single feeder system. The rhythmic, fine-grained, and thinly laminated quartzite is interpreted as having been produced by the consecutive filling, under high fluid pressure, of a cavity with quartz and the oldest detectable scheelite mineralization (stage 1 scheelite), periodically interrupted by detachment and sliding phenomena. The feeder system narrows downwards as its WO 3 grade diminishes. The western ore field consists of several orebodies (K 1 to K 8 ). In the K 2 orebody, the emplacement of an I-type granite (older K 2 gneiss: 525 ± 14 Ma) was followed by the deposition of a bowl-shaped quartz mass and the formation of an eruption breccia (510 ± 36 Ma), intruded by a younger granite dike (younger K 2 gneiss: 512 ± 10 Ma). Primary scheelite deposition was coeval with the formation of the quartz mass; it was strongly enhanced during the formation of the eruption breccia, accompanied by elevated F contents, but was only minor in the subsequent intrusion of the small, younger K 2 granite. Primary mineralizing fluids are not preserved in fluid inclusions of scheelite due to metamorphic overprints. However, they may still be characterized by isotopic data of scheelite, which reflect a crustal origin with 87 Sr/ 86 Sr = 0.72 to 0.74, negative ε Nd ratios, elevated 238 U/ 204 Pb ( 206 Pb/ 204 Pb, 207 Pb/ 204 Pb) ratios, δ 18 O values of 8 per mil, as well as enrichments in Rb and Cs. Significant contributions to the fluids were possibly released from micas due to breakdown, leaching, or restructuring reactions, which may occur in deeper sections of a thick continental crust at an active continental margin setting. Such fluids apparently infiltrated a magma chamber of the Habach Group rock suite and caused the subsolidus formation of tschermakitic hornblende (with 87 Sr/ 86 Sr ratios of 0.74) by replacing clinopyroxene (with 87 Sr/ 86 Sr ratios of 0.707). Eventually, they transferred a presumably dissolved W content into the melt. There is no clear geologic record from the time interval between the early Paleozoic (Cambrian) and the emplacement of the late Paleozoic Habach intrusive rocks. One of the latter is represented in the western ore field of the Felbertal scheelite deposit by a horseshoe-shaped granite gneiss intrusion in the K 1 and K 3 orebodies, dated at 336 ± 19 Ma. The total mass of these K 1 -K 3 gneisses is approximately 5 million tons. The gneisses display geochemical and isotopic characteristics of a differentiated, orogenic melt of mixed crust-mantle origin. This melt may have been produced by the injection of mantle-derived magmas into a (thick) continental crust, presumably during a period of crustal relaxation. There is evidence for a K 1 -K 3 granite-related scheelite deposition in these granites, in apical quartz masses, and in their host rocks (mainly fine-grained amphibolites) in the form of quartz veins and small veinlets that are as much as tens of meters from the granite contact. Variscan amphibolite facies metamorphism between 325 and 280 Ma induced a period of pervasive remobilization and caused an ubiquitous, low-grade dispersion of the preexisting early and late Paleozoic scheelite mineralization and the formation of some high-grade enrichments of scheelite porphyroblasts along shear zones (stage 2 scheelite). Several sets of crosscutting, scheelite-bearing quartz veins and veinlets were formed under protracted amphibolite-facies metamorphic conditions. The metamorphic fluid regime further induced an alteration of the geochemical patterns of preexisting rocks (e.g., enrichments of Rb and Cs as well as of U, and 207 Pb, compared to Th, and 208 Pb). Furthermore, elevated 87 Sr/ 86 Sr ratios, possibly released from micas, dominated the isotopic signature of the recrystallizing, metamorphic scheelites. Small lamprophyric dikes were emplaced in Late Variscan time after the intrusion of the Granatspitze central gneiss protoliths, the emplacement of the K 1 -K 3 granite, and the subsequent shear zone formation. A change of the previously prevailing oxidizing conditions occurred, presumably after the intrusion of the lamprophyres. Subsequently, strong reducing conditions are indicated by WS 2 -MoS 2 exsolutions in the preexisting stage 1 and stage 2 “molybdoscheelites.”These scheelites were followed by the coexistence of MoS 2 and of bluish, fluorescent, pure scheelites (stage 3 scheelite), the crystallization of which has been dated by Sm-Nd at 319 ± 34 Ma. Evidence for the reducing conditions during the Late Variscan tungsten remobilization period is provided by a methane component in the fluid inclusions within such scheelites and accompanying quartz. Under Alpine lower amphibolite- to upper greenschist-facies metamorphic conditions, the scheelite remobilization was obviously less intense. It was locally focused along some faults and quartz veins, usually as sparse, but large, whitish-bluish fluorescent crystals with a Sm-Nd age of 29 ± 17 Ma (stage 4 scheelite).