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

More documents

Recommendations

Info

90 GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1992 Sleetmute, Russian Mission, Taylor Mountains, and Bethel quadrangles, southwestern Alaska: Alaska Division of Geo- logical and Geophysical Surveys Public-Data File 86-99, 9 P. Sainsbury, C.L., and MacKevett, E.M., Jr., 1965, Quicksilver deposits of southwestern Alaska: U.S. Geological Survey Bul- letin 1187, 89 p. Theodorakos, P.M., Borden, J.C., Bullock, J.H., Jr., Gray, J.E., and Hageman, P.L., 1992, Analytical data and sample locality map of stream-sediment and heavy-mineral-concentrate samples collected from the Horn Mountains area, Sleetmute quadrangle, southwest Alaska: U.S. Geological Survey Open-File Report 92-708-A, 36 p. Welsch, E.P., 1983, A rapid geochemical spectrophotometric de- termination of tungsten with dithiol: Talanta, v. 30, p. 876- 878. Reviewers: Karen D. Kelley and Richard J. Goldfarb
GOLD AND CINNABAR IN HEAVY-MINERAL CONCENTRATES FROM STREAM-SEDIMENT SAMPLES COLLECTED FROM THE WESTERN HALF OF THE LIME HILLS 1" x 3" QUADRANGLE, ALASKA ABSTRACT Geochemical sampling in the western half of the Lime Hills 1" x 3" quadrangle has revealed the presence of visible gold and cinnabar in numerous heavy-mineral-concentrate samples. This widespread fine-grained gold has not been reported previously. Further, there are no mines or prospects in the area. The area is underlain predominantly by clastic rocks of the post-accretionary Cretaceous Kuskokwim Group and by Paleozoic clastic and carbonate rocks of the Dillinger, Mystic, and Nixon Fork terranes. Gold was identified in 100 of the 396 heavy-mineral concentrate samples collected. Megascopic gold was observed in 30 samples, the largest grain being about 1 mm in diameter. Gold grains usually are less than 0.3 mm in the longest dimension. The grains are commonly flat and rounded to subrounded, and less frequently are elongate. Less commonly, gold grains have delicate shapes with an- gular or jagged edges, embayments, and protrusions. Euhedral gold grains were not observed. The variations in gold grain morphology may indicate distal and local sources for the gold. Anhedral cinnabar was identified in 45 of the concentrate samples. Megascopic grains of cinnabar rarely were observed. Cinnabar grain size typically is in the range of a few tenths of a millimeter. Two distinct sample populations are evident. Samples in the northern half of the study area contain cinnabar 2 gold. This area is underlain almost entirely by carbonate and clastic rocks of the Dillinger terrane. Diorite, granite, granite porphyry, and quartz porphyry are common in alluvium, but rare in outcrop in the area. The cinnabar r gold in concentrates may reflect small epithermal cinnabar- and stibnite-bearing vein deposits such as those found else- where throughout southwestern Alaska. Samples in the southern half of the study area contain gold, but generally lack cinnabar. The southern area is underlain by platform carbonate rocks of the Nixon Fork terrane and marine clastic rocks of the Kuskokwim Group. As in the northern part of the study area, igneous rocks are By Robert G. Eppinger common in alluvium, but rare in outcrop. The presence of gold and paucity of cinnabar in concentrates in the southern area suggest an origin different from that of the cinnabar k gold in concentrates to the north. INTRODUCTION A geochemical survey of the Lime Hills lo x 3" quadrangle is in progress by the U.S. Geological Survey, as part of the Alaska Mineral Resource Assessment Program (AMRAP). Reconnaissance sampling in the western half of the quadrangle was undertaken during the summers of 1991 and 1992 (fig. 1). This sampling has revealed visible gold and cinnabar in numerous heavy-mineral-concentrate samples collected from stream sediment. There are no published reports of widespread gold occurring in this area. Geochemical studies of the samples collected in the study area are in progress. Previous work in the quadrangle includes geologic mapping, stream-sediment geochemical surveys, and geo- chronologic studies in the Alaska Range (Reed and Elliot, 1970; Reed and Lanphere, 1969, 1972, 1973; and Lanphere and Reed, 1985) and mapping and geochemical studies in the northwestern part of the quadrangle (Gilbert, 1981). Geochemical studies of the quadrangle were undertaken during the National Uranium Resource Evaluation (NURE) program (Jacobson and others, 1979; Hinderman, 1982). Geochemical data for samples collected in the east- em half of the Lime Hills quadrangle as part of the AMRAP program are reported in Allen and others (1990), Allen and Slaughter (1990), Malcolm and others (1990), and Motooka and others (1990). These geochemical data were used in an interpretive report on gold anomalies and occurrences in the eastern half of the Lime Hills quadrangle (Allen, 1990). Terrain in the western half of the Lime Hills quadrangle consists dominantly of heavily vegetated, swampy lowlands with elevations of 300 m or less. Interspersed among these areas are small, rolling, mountainous areas,
Page 1 and 2:
Geologic Studies in Alaska by the U
Page 3 and 4:
CONTENTS Introduction Cynthia Dusel
Page 5 and 6:
CONTENTS CONTRIBUTORS TO THIS BULLE
Page 7 and 8:
GEOLOGIC STUDIES IN ALASKA BY THE U
Page 9 and 10:
LATE HOLOCENE LONGITUDINAL AND PARA
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
DEEP-WATER LITHOFACIES AND CONODONT
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Table 1. Locality register for key
Page 27 and 28:
Table 1. Locality register for key
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
LITHOFACIES AND CONODONTS OF CARBON
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46: LITHOFACIES AND CONODONTS OF CARBON
Page 49 and 50: LITHOFACES AND CONODONTS OF CARBONI
Page 51 and 52: Table 1. Conodont faunules and lith
Page 55 and 56: DEPOSITIONAL SEQUENCES IN ATIGUN SY
Page 65 and 66: U-Pb AGES OF ZIRCON, MONAZITE, AND
Page 77 and 78: APPEAL FOR NONPROLIFERATION OF ESCA
Page 85 and 86: FAVORABLE AREAS FOR METALLIC MINERA
Page 95: FAVORABLE AREAS FOR METALLIC MINERA
Page 99 and 100: GOLD AND CINNABAR IN HEAVY-MINERAL
Page 107 and 108: EARLY CENOZOIC DEPOSITIONAL SYSTEMS
Page 111 and 112: EARLY CENOZOIC DEPOSITIONAL S YSTEM
Page 125 and 126: RESERVOIR FRAMEWORK ARCHITECTURE, C
Page 137: GEOCHEMISTRY OF OPHIOLITIC ROCKS FR
Page 140 and 141: 134 GEOLOGIC STUDIES IN ALASKA BY '
Page 142 and 143: 136 GEOLOGIC STUDIES IN ALASKA BY T
Page 144 and 145: 138 GEOLOGIC STUDIES IN ALASKA BY T
Page 146 and 147:
140 GEOLOGIC STUDIES IN ALASKA BY T
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
GEOLOGIC STUDIES IN ALASKA BY THE U
Page 156 and 157:
1 150 GEOLOGIC STUDIES IN ALASKA BY
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165:
Page 166 and 167:
Page 168 and 169:
Page 170 and 171:
1 64 GEOLOGIC STUDlES IN ALASKA BY
Page 172 and 173:
166 GEOLOGIC STUDES IN ALASKA BY TH
Page 174 and 175:
Page 176 and 177:
Page 178 and 179:
Page 180 and 181:
Table 1. Isotopic ages of intrusive
Page 182 and 183:
Table 1. Isotopic ages of intrusive
Page 184 and 185:
GEOCHEMICAL EVALUATION OF STREAM-SE
Page 186 and 187:
Page 188 and 189:
Page 190 and 191:
Page 192 and 193:
Page 194 and 195:
Page 196 and 197:
Page 198 and 199:
Page 200 and 201:
Page 202 and 203:
Page 204 and 205:
Page 206 and 207:
20 GEOLOGIC STUDIES IN ALASKA BY TH
Page 208 and 209:
Page 210 and 211:
Page 212 and 213:
Table 3. Summary of geochemical sig
Page 214 and 215:
Page 216:
Page 219 and 220:
GEOCHEMICAL CHARACTER OF UPPER PALE
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
RECONNAISSANCE GEOCHEMISTRY OF BASA
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
Page 235 and 236:
OSTRACODE ASSEMBLAGES FROM MODERN B
Page 237 and 238:
Page 239 and 240:
Page 241 and 242:
Page 243 and 244:
RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
Page 245 and 246:
RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
Page 247 and 248:
US. GEOLOGICAL SURVEY REPORTS ON AL
Page 249 and 250:
U.S. GEOLOGICAL SURVEY REPORTS ON A
Page 251 and 252:
U.S. GEOLOGICAL SURVEY REPOR TS ON
Page 253 and 254:
REPORTS ABOUT ALASKA IN NON-USGS PU
Page 255 and 256:
REPORTS ABOUT ALASKA IN NON-USGS PU
show all

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

Create successful ePaper yourself

Delete template?

Save as template?