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Evidence for the Crescent Valley- Independence Lineament, North-Central Nevada

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Evidence for the Crescent Valley- Independence Lineament, North-Central Nevada CONTRIBUTIONS TO THE GOLD METALLOGENY OF NORTHERN NEVADA OPEN-FILE REPORT 98-338 EVIDENCE FOR THE CRESCENT VALLEY- INDEPENDENCE LINEAMENT, NORTH-CENTRAL NEVADA By Stephen G. Peters ABSTRACT deformation, igneous intrusion, and hydrothermal activity were focused along the lineament periodically between the late The Crescent Valley-Independence lineament (CVIL) in Paleozoic and middle Tertiary. north-central Nevada is defined by deformation, igneous Many sedimentary rock-hosted gold deposits in north- intrusions, and hydrothermal activity of several ages along a central Nevada cluster in mining districts that lie along N20E- to N30E-striking zone. This zone extends for about 90 northwest-trending belts (Roberts, 1960, 1966; Thorman and km from near the Independence Mining District in the north Christensen, 1991), or are associated with regional-scale to near the Cortez Mine in the south. The center parts the lineaments (see Shawe, 1991). Belts and lineaments are CVIL mark the southeastern edge of the Tuscarora Mountains compatible with genetic theories of sedimentary-rock-hosted near the gold deposits along the Carlin trend. The southwestern gold deposit ore formation, which call for deep-seated, over- part extends through Crescent Valley and the Cortez-Pipeline pressured fluids and associated conduits (Kuehn and Rose, Mining District. 1995; Lamb and Cline, 1997). Alignment of these and other The CVIL is well exposed along its center segment in gold ore bodies has been suggested by Shawe (1991) to be an the Bob’s Flat, Richmond, and the Carlin Mine areas where it important factor in producing the large crustal endowment of contains intensely tectonized rock of the upper-plate of the gold in Nevada. Lineaments have been postulated to be the Roberts Mountains allochthon, probably Ordovician Vinini main conduits for deep-sourced metal-bearing fluids (Kerrich, Formation, northeast-striking faults, or Cretaceous or Tertiary 1986; Kerrich and Kyser, 1994) and may interact with these northeast-striking dikes. Fabrics in deformed zones have fluids near or in the ore depositional environment (Phillips, characteristics of mélange that also exhibit fabric orientation 1986; Henley and Ethridge, 1994; Hickman and others, 1994). parallel to fold orientations that result from deformation between the late Permian and late Jurassic (Sonoma and Elko orogenies). In addition, Tertiary-age jasperoid, breccia, calcite GENERAL GEOLOGY veins, and decalcification locally are present along the CVIL. Clusters of sedimentary rock-hosted gold deposits in the north Reconstructions of the tectonic history of north-central and south ends of the CVIL contain several mineralogical Nevada indicate that early and middle Paleozoic, deep-water features common to deposits in the Carlin trend area. All the sedimentary and igneous rocks were thrust eastward districts contain northeast-striking faults that cross cut tectonic approximately 75 to 200 km during the Late Devonian to Early windows and structural highs through the upper-plate of the Mississippian Antler orogeny (Roberts, 1958; Roberts, 1964). Roberts Mountains allochthon. The CVIL may be a major These rocks compose the Roberts Mountains allochthon, which fluid conduit that was instrumental in formation of some of lies upon coeval shallow-water rocks of the continental the gold deposits. platform. The two packages of rocks, the upper and lower- plates, are separated by the Roberts Mountains thrust (Merriam and Anderson, 1942; Roberts and others, 1958). Emplacement INTRODUCTION of the allochthon produced a topographic high, which shed sediments, that constitute the overlap assemblage of rocks, to This paper presents geologic and geomorphologic the east and west in the late Paleozoic (Roberts, 1960; Madrid evidence for the Crescent Valley-Independence lineament and others, 1992), and were followed by local volcanism in (CVIL) in north-central Nevada, a 90–km-long tectonic feature the early Mesozoic (fig. 1). Other tectonic reconstructions that intersects three major sedimentary rock-hosted gold suggest that some geologic relations in the region also may be districts, the Cortez-Pipeline, Carlin, and Independence Mining due to: (1) local Early Triassic remobilization of the Roberts Districts (fig. 1). Geologic features recognized in the center Mountains allochthon (Ketner and Alpha, 1992; Ketner and part of the CVIL, near the Carlin trend, suggest that others, 1993); (2) significant tectonism in the region during 106 CARLIN-TYPE GOLD DEPOSITS o o 117 116 ° ° 118 117 116° 115° 114° N 42° Independence Carlin 41° Independence Pipeline-Cortez 40° Mining District 0 10 miles 39° (16 km) yyy Nevada yyyyyyy o 41 Area of Carlin Fig.7 trend Area of Area of Fig.6 yFig.4 yyy Explanation Sedimentary and yy yyvolcanic rocks Cortez-Pipeline (Late Tertiary) Volcanic rocks (Early Tertiary) Upper-plate rocks (Lower Paleozoic) yyyyyyy Lower Paleozoic o 40 lower-plate rocks Upper Paleozoic and Mesozoic rocks Sedimentary rock- hosted gold deposit yyyyy Figure 1. Location of the Crescent Valley-Independence lineament (CVIL) in north-central Nevada. The main focus of the lineament is indicated by the northeast-trending, partially dashed, black line that intersects the Independence, Carlin and Cortez- Pipeline Mining Districts. Note location of figures referred to in text, Bob’s Flat, Richmond, and Carlin Mine. (Geology simplified from Stewart and Carlson, 1976). 107 y CONTRIBUTIONS TO THE GOLD METALLOGENY OF NORTHERN NEVADA OPEN-FILE REPORT 98-338 the Late Jurassic Elko orogeny; (3) the Cretaceous to Early Tertiary Sevier orogeny; and (4) large-scale extensional INDEPENDENCE detachment faulting in the late Eocene to early Oligocene DISTRICT (Thorman and others, 1991a, b; Seedorff, 1991; Wallace, 1991). Orientation, nature, and geometric relations among tectonic fabrics in and near the CVIL may constrain the timing of events along it. Most fold axes in Paleozoic rocks in north- central Nevada plunge at low angles to the northeast and southwest (Evans and Theodore, 1978; Oldow, 1984; Peters and Evans, 1996). These folds have axial planes and fold BCF axes that are roughly parallel to the CVIL; however, fold axes near major mineralized trends plunge at shallow angles to the northwest (Madrid, 1987; Madrid and Bagby, 1986; Peters, 1996, 1997a). The northwest-trending fold axes along the GOLDSTRIKE Carlin trend were postulated by Evans and Theodore (1978) MINE to be due to Jurassic tectonism, which apparently is synchronous with some tectonic events recognized by Ketner and Smith (1982), Ketner (1987) and Thorman and others C (1991a) in northeastern Nevada. This implies that much of the northeast-trending tectonic fabric in the CVIL predates BEOWAWE R the Jurassic; however, as detailed below, younger geologic MELANGE events may also have northeast orientations in the CVIL. The CVIL is defined by a N20E- to N30E–striking zone BF GOLD QUARRY of linear geologic and geomorphologic features. As defined MINE here, the lineament is present in the north on the west side of the Independence Mountains, on the east side of Independence Valley, and may include parts of the Independence Mining District (fig. 1). Farther to the southwest it marks the southeast edge of the Tuscarora Mountains near the Carlin trend. In its central parts, the CVIL passes through rocks of the Ordovician Vinini Formation in the southern Tuscarora Mountains near Figure 2. Annotated Landsat image of the northern part of the Boulder Valley and Bob’s Flat. It then continues south through Crescent Valley-Independence lineament. Topographic features have Beowawe on the northeast side of Crescent Valley and may been highlighted with dark lines. Using this image, the composite extend into Carico Lake Valley and farther to the southwest. lineament zone is approximately 20 km wide, and contains three strands each of which may be 2 to 3 km wide. Large mines shown The central parts of the CVIL constitute a 3- to 5-km- for location. BF, Bob’s Flat; R, Richmond, C, Carlin Mine. BCF, wide zone that may, in part, be part of a much larger, composite Boulder Creek fault segment (from Theodore and others, this volume) 20-km-wide zone containing additional northeast-trending of larger photo-linement. Field of view approximately 77 by 144 linear features (fig. 2). The CVIL also roughly marks the km western edge of a 80–km-wide Tertiary basin lying between the Independence and Ruby Mountains (see Regina, 1960; of calcareous host rocks, typify. Because of the spatial and Stewart and Carlson, 1976; Solomon and others, 1979; temporal relation to the three mining districts, it is possible Mueller, 1992). The northern projection of CVIL marks the that some geologic features present in the CVIL could have eastern edge of the Boulder batholith (see Muehlberger, 1992), formed synchronous with the deposits. suggesting that it may be part of a larger crustal-scale feature. The importance of the CVIL for gold ore genesis is that it traverses or is adjacent to three major sedimentary-rock-hosted CHARACTER, TERMS, AND GENESIS OF gold mining districts that have deposit styles and mineralogic MÉLANGE ROCKS ALONG THE CVIL characteristics of sedimentary-rock-hosted gold (“Carlin- type”) deposits (Kuehn and Rose, 1995; Arehart, 1996; see Rock types near and in the CVIL contain fabrics that are also Peters and others, 1996). These characteristics are typical of mélange zones (see Peters, 1996, 1997a). Mélange arsenian rims on older pyrite, presence of late orpiment, is a mappable body of fragmented and mixed rock, with realgar, and stibnite, and alteration minerals assemblages phacoidal shapes, in a scaly, shaley matrix, commonly called formed during decalcification, carbonation and argillitization clast-in-matrix rock or brokenite (Raymond, l984a, b; Peters, 108 CARLIN-TYPE GOLD DEPOSITS 1993). The chaotic nature of mélange is caused by either margins commonly are anastomosing or conjugate shear sedimentary or tectonic processes that produce zones where strain and fluid has been partitioned around the fragmentation, mixing, disruption, and dismemberment. undeformed phacoidal-shaped rocks, although they Although the laws of lateral continuity and superposition commonly retain internal symmetry (fig.
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