Geologic description
The dominant lithology at the Pika Canyon prospect is augen gneiss having a possible igneous protolith (Mertie, 1931; Foster, 1970). This protolith has a possible emplacement age (inferred from dating other exposures in the region) of Devonian to Mississippian (360 Ma), with resets in the Late Jurassic (190 Ma) and Early to Mid-Cretaceous (135-107 Ma) time (Dusel-Bacon and Aleinikoff, 1985). A series of plugs and dikes which range in composition from diorite to monzodiorite intrude the augen gneiss. Based on cross-cutting relationships and minimal alteration within these units, these intrusions are interpreted to be syn- to post-mineralization in age. The mapped intrusions directly correspond with magnetic highs in the regional 1:50,000 scale magnetic survey conducted by Full Metal Minerals-BHP Billington (King and Tedeschi, 2012). Based on similarities to nearby dated plutons, the Pika Canyon intrusions are likely members of the Prospector Mountain Suite formed during the development of a volcanic arc during the Late Cretaceous (Selby and Creaser, 2001). The alteration in the greater Pika Canyon area is patchy and somewhat irregular, but generally occurs in somewhat concentric zones of potassic, phyllic, and propylitic alteration (Gill, 1977). Significant brecciation and extensive alteration occurs along the contact of the diorite dike with the augen gneiss located in the saddle of Pika Canyon, indicating it was a conduit for hydrothermal fluids. Mineralization at Pika Canyon consists of gold-silver rich quartz vein stockwork in augen gneiss at and near the contact with the diorite dike. Alteration of the augen gneiss is zoned based on distance from the diorite contact. Distally, alteration is weak consisting of biotite destruction replaced by fine grained sericite and iron oxides. Weak alteration grades into strong to moderate sericite and silicification towards the contact. Silicification is most commonly manifested as thin sheeted veins and stockwork exploiting foliation, but occasionally crosscuts primary fabric, including augens. These foliation parallel veins range in thickness from 1 to 10 millimeters and occasionally contain jarosite and iron oxides, indicative of the former presence of sulfide minerals. Typically these veins are clear to bluish in color and are very fine grained (King and Tedeschi, 2012). |
Alteration of deposit |
The alteration in the greater Pika Canyon area is patchy and somewhat irregular, but generally occurs in somewhat concentric zones of potassic, phyllic, and propylitic alteration (Gill, 1977). In the saddle of Pika Canyon alteration of the augen gneiss is zoned based on distance from the diorite contact. Distally, alteration is weak consisting of biotite destruction replaced by fine grained sericite and iron oxides. Weak alteration grades into strong to moderate sericite and silicification towards the contact. Silicification is most commonly manifested as thin sheeted veins and stockwork exploiting foliation, but occasionally crosscuts primary fabric, including augens (King and Tedeschi, 2012). |