Geologic description
As described by Brooks (1902), the deposit at the Hope prospect is a quartz vein about 2 feet thick that contains free gold, pyrite, and minor chalcopyrite. The deposit was prospected by a 20-foot tunnel and several pits. A sample of the vein contained $40 per ton in gold (at $20.67 per ounce). A sample of a 12-foot-wide surface exposure of the vein contained abut $38 per ton in gold. Wright and Wright (1908) also examined the prospect, but gave few details beyond indicating that the vein is in chlorite schist near a large granitic intrusion. This contradicts Brooks, who reported that the vein is in silicified diorite porphyry. Maas and others (1992) identified a quartz vein in blocky greenstone that could be traced for about 90 feet in a short adit, trenches, and open cuts. Their samples contained 23 to 2,506 parts per million (ppm) copper, 12 ppm to 4.76 ounces of silver per ton, and 939 parts per billion to 1.487 ounces of gold per ton. The age of the rocks in the area has been variously interpreted. Eberlein and others (1983) mapped the strata as locally metamorphosed graywacke of Silurian or Ordovician age, near a large Paleozoic or Mesozoic granitic intrusion. Gehrels (1992) and Maas and others (1995) mapped them as pre-Ordovician metamorphosed volcanic and sedimentary rocks near a Silurian or Ordovician granitic intrusion. Brew (1996) called them Late Proterozoic and Cambrian Wales Group schist, phyllite, and marble, near a Tertiary granitic intrusion of intermediate composition. Most recently, Slack and others (2002) and S.M. Karl (oral communication, 2003) mapped the strata as Silurian and Ordovician, low-grade, regionally metamorphosed sedimentary and volcanic rocks. |
