Shamrock (ARDF #RM042) Au, Bi, Cu, Mo

Shamrock

Prospect, Active

Commodities and mineralogy

Main commodities	Au; Bi; Cu; Mo
Ore minerals	bismuthinite; chalcopyrite; gold; molybdenite; pyrite
Gangue minerals	calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale	RM
Quadrangle map, 1:63,360-scale	A-3
Latitude	61.0364
Longitude	-159.8621
Nearby scientific data	Find additional scientific data near this location
Location and accuracy	Shamrock Creek is a south-flowing tributary to Bear Creek in the Nyac area. The coordinates are at about the center of the area that was drilled in 2005 and 2006; the site is about 0.6 mile northeast of section 23, T. 11 N., R. 60 W., of the Seward Meridian. It is unclear how much of the creek will be mined, but the drilling continued for about 0.8 mile above and below this point on the creek. Mining began near the upper end of the drilling in August 2006, but more drilling is likely or has already been done above the mining. The location is probably accurate to within 1,000 feet.

Geologic setting

Geologic description This record is about the lode prospect near Shamrock Creek placer (RM039). The host rock at Shamrock is Jurassic volcanic and volcaniclastic rock that has undergone mesothermal alteration. Mesothermal facies developed in the Nyac host rock are pervasive propylitic, hornfelsic, and silicic alteration, along with silica-sericite selvages enveloping mesothermal veins, veinlets, and fractures. Brown biotite hornfels developed in the andesitic volcanics represent a higher degree of mesothermal alteration, surrounded by pervasive greenish quartz-calcite-chlorite propylitic alteration (Strachan, 2008). Mineralization occurs in auriferous quartz-calcite-pyrrhotite-chalcopyrite-pyrite veins and veinlets. Another vein type with a mineral assemblage associated with gold is quartz-chlorite-calcite-pyrite-chalcopyrite-bismuthinite-molybdenite-native gold. These veins and veinlets are later than the pervasive sericitic alteration. Silica selvage is well developed away from the vein in biotite hornfels (Strachan, 2008).
Geologic map unit	(, )
Mineral deposit model	Low-sulfide gold-quartz vein (Cox and Singer, 1986; model 36a).
Mineral deposit model number	36a
Age of mineralization	Probably mid-Cretaceous as at the Bonanza Ridge prospect, ARDF number RM037 (Wenz, 2004, 2005).
Alteration of deposit	The host rock at Shamrock is Jurassic volcanic and volcaniclastic rock that has undergone mesothermal alteration. Mesothermal facies developed in the Nyac host rock are pervasive propylitic, hornfelsic, and silicic alteration, along with silica-sericite selvages enveloping mesothermal veins, veinlets, and fractures. Brown biotite hornfels developed in the andesitic volcanics represent a higher degree of mesothermal alteration, surrounded by pervasive greenish quartz-calcite-chlorite propylitic alteration (Strachan, 2008).

Production and reserves

Workings or exploration	Systematic geochemical surveys have been completed in the Nyac Gold District by many entities, including Research Associates of Alaska, Placer Dome Exploration, Calista Native Corporation, Zachary Wenz, and Tonogold Resources, Inc. These surveys included collection and assaying of rock chip, soil, stream, alluvial, and pan concentrate samples (Strachan, 2008). In 2005-2006, Tonogold Resources Inc. explored for the bedrock source of gold from the productive drainages near active placer Shamrock Creek (RM039). This effort included outcrop mapping and sampling. 3,149 grid soils samples collected in 2005 resulted in 323 (10.3 percent) assaying more than 0.1 parts per million (ppm) gold. 3,594 samples collected in 2006 resulted in 122 (5.2 percent) assaying over 0.1 ppm gold (Strachan, 2008). In 2013, Nyac Gold LLC conducted prospecting, drilling, sampling, and petrographic work at Shamrock Creek in order to determine the extent of and complex nature of the intrusive and gold mineralization (Flanders, 2013).
Indication of production	None
Additional comments Mining on the placer Shamrock Creek (RM039) began in August 2006 (Strachan, 2008).

References

References Box, S. E, Moll-Stalcup, E. J., Frost, T. P., and Murphy, J. M., 1993, Preliminary geologic map of the Bethel and southern Russian Mission quadrangles, southwestern Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2226-A, 20 p., scale 1:250,000. Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, 379 p.
Reporters	V.C. Zinno (Alaska Earth Sciences, Inc.)
Last report date	3/15/2016