Geologic Studies in Alaska by the U.S. Geological Survey, 1992

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154 GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAI, SURVEY, 1992 2.5 km along the Contact fault. However, the part of the pluton south of the fault is granite, but the part to the north is gabbro. We are uncertain how these two composition- ally different parts of the pluton are structurally related. Northeast-southwest-striking faults cut and displace the Terentiev Lake and Cedar Bay plutons (fig. 2). A fault that cuts the Terentiev Lake pluton is nearly vertical and has about 30 m of apparent southeast-side-up motion. The fault that cuts the Cedar Bay pluton is not exposed, but the topography on the northwest side of the fault is about 100 m lower than that on the southeast side, which suggests that its motion is also southeast-side-up. This fault is at least 12 km long and is the structural boundary between domain D on the northwest and domains F and H on the southeast. QUARTZ VEINS Quartz veins are found throughout the study area and typically dip steeply and strike north-south or NNW-SSE (fig. 14). We noted no veins parallel to bedding or cleav- age as reponed by Goldfarb and others (1986) in rocks of the Valdez Group. The quartz veins are generally less than 2 cm wide, but some are up to 2 m. Some veins are planar and contain coarsely crystalline quartz, in contrast to - 0 5 CENTIMETERS Figure 10. Polished slab of granitic autobreccia from others that are planar and have dendritic offshoots or are a series of en echelon tension fractures. There was no dis- cernible shearing across most veins. STRUCTURAL GEOLOGY OF MINEML OCCURRENCES BLACKJACK PROSPECT The two prospects in the study area from which we have the most structural information are the Blackjack and the Columbia Red Metals (fig. 2) (Jansons and others, 1984). The Blackjack is the largest epigenetic zinc prospect in Prince William Sound and is hosted by the Cedar Bay pluton. It consists of an east-west trending adit about 90 m long with a small (53 m to the east and to the west) drift along a 1.5-m-wide silicified zone striking northsouth, located a few meters from the end of the main drift. Within the silicified zone, the tonalitic host rock has been recrystallized into fine-grained medium-gray material that is iron stained on most surfaces. There has been no exploration along similar, but narrower (
STRUCTURAL EVOLUTION OF THE CHUGACH-PRINCE WILLIAM TERRANE 155 3 cm of gouge and with subhorizontal mullions, indicating strike-slip motion. We were unable to determine the sense of slip on this surface. In a 15-m-long upper adit, there has been probable left-lateral offset on structures with the same orientation. There was no other evidence for high strain within the mineralized zone, as there was no planar or linear fabric. The mineralizing fluids apparently followed pre-existing joints or faults. Jansons and others (1984) reported that the mineralized zone is traceable for 1.5 krn. COLUMBIA RED METALS PROSPECT The Columbia Red Metals prospect is a rust-weather- ing polymetallic vein occurrence located along the Miners Bay-Kadin Lake splay of the Contact fault (fig. 2); it lies within graywacke of the Orca Group, and conglomerate is present within and adjacent to the prospect. A small disseminated sulfide-bearing felsic stock and a dike are lo- Faults, type unknown ?J Dextral faults N Reverse faults N Sinistral faults N cated less than 0.5 km to the east. The mineralized zone is about 1 m thick and strikes 015" and dips 52" E. (fig. 15). It contains brecciated wall rock inclusions and planar zones of chalcopyrite with lesser pyrite, limonite, iron ox- ides and (or) Fe-S oxyhydroxides. Jansons and others (1984) also reported disseminated galena and sphalerite. They were able to trace the sulfide-bearing part of the occurrence 65 m along strike. The chalcopyrite is ribboned in places. Also within and adjacent to the mineralized zone are drusy quartz crystals up to a centimeter across and 2 cm long. Jansons and others (1984) described this occurrence as a shear zone. However, we found no evidence for differential slip within or along the walls of the mineralized zone. Adjacent to the mineralized zone there is a dendritic network of barren quartz veinlets (figs. 15 and 16); veinlets are less than a centimeter thick and locally surround blocks of wall rock less than 15 cm across. These veins are most abundant within several meters of the mineralized zone. Normal fault N Poles to all faults N Figure 12. Equal-area stereograms of faults in study area. Dots show slip direction on faults in which it could be determined. Contoured plot is a Karnb contoured plot of poles to all faults. C.I., contour interval; N, number of samples.
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Geologic Studies in Alaska by the U
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CONTENTS Introduction Cynthia Dusel
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CONTENTS CONTRIBUTORS TO THIS BULLE
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GEOLOGIC STUDIES IN ALASKA BY THE U
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LATE HOLOCENE LONGITUDINAL AND PARA
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DEEP-WATER LITHOFACIES AND CONODONT
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Table 1. Locality register for key
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Table 1. Locality register for key
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LITHOFACIES AND CONODONTS OF CARBON
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LITHOFACES AND CONODONTS OF CARBONI
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Table 1. Conodont faunules and lith
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DEPOSITIONAL SEQUENCES IN ATIGUN SY
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U-Pb AGES OF ZIRCON, MONAZITE, AND
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APPEAL FOR NONPROLIFERATION OF ESCA
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FAVORABLE AREAS FOR METALLIC MINERA
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GOLD AND CINNABAR IN HEAVY-MINERAL
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EARLY CENOZOIC DEPOSITIONAL SYSTEMS
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Table 3. Summary of geochemical sig
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GEOCHEMICAL CHARACTER OF UPPER PALE
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RECONNAISSANCE GEOCHEMISTRY OF BASA
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OSTRACODE ASSEMBLAGES FROM MODERN B
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RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
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RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
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US. GEOLOGICAL SURVEY REPORTS ON AL
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U.S. GEOLOGICAL SURVEY REPORTS ON A
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U.S. GEOLOGICAL SURVEY REPOR TS ON
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REPORTS ABOUT ALASKA IN NON-USGS PU
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REPORTS ABOUT ALASKA IN NON-USGS PU
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Geologic Studies in Alaska by the U.S. Geological Survey, 1992

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