|Quadrangle map, 1:250,000-scale||TC|
|Quadrangle map, 1:63,360-scale||D-1|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The South Pika prospect, formerly called the Fishhook prospect, is located in a saddle northeast of hill 4455 at the headwaters of the Sixtymile River, west of Fishhook Bend. The prospect location has been updated from previous reporting to where a northeast trending gold soil anomaly was trenched in the northeast corner of section 4, T. 23 N., R. 21 E. of the Copper River Meridian.|
The dominant lithology within the South Pika prospect area 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). Cretaceous-Tertiary, fine-grained biotite granite, granodiorite, monzodiorite, and a coarse-grained alkali granite intrude the augen gneiss and are exposed in small outcrops at the prospect. Tertiary (?) volcanics are also present (Gill, 1977).
Local structures are dominated by numerous, high-angle, northeast-trending fault zones. Many subordinate fault zones in the area parallel the northeast strike and possibly reflect underlying igneous activity (Curt Freeman, unpublished data, 1998). A prominent northeast-trending fault cross-cutting South Pika is characterized by pervasive silicification and rare hydrothermal breccias, surrounded by a broader zone of strong clay alteration of feldspar augen porphyroblasts and matrix feldspar. Surrounding the clay alteration is a narrow zone of sericite alteration where schistose matrix biotite has been replaced by fine-grained muscovite. Reverse faults of unknown age are interpreted where graphitic and actinolite-chloritic schists are exposed (Siron and Grady, 2011).
The mineralization at South Pika appears to be structurally controlled by the northeast trending faults. Minerals include chalcopyrite, galena, gold, molybdenite, pyrite, silver, sulfosalts, and stibnite. The more highly mineralized areas occur as breccias along the northeast-trending faults. The Cretaceou-Tertiary plutonic rocks also contain elevated values of lead, silver, barium, antimony, and gold. Anomalous bismuth along some of the faults suggests a plutonic-source fluid (Curt Freeman, unpublished data, 1998). The strongly silicified augen gneiss at the core of the alteration zones exhibit a variety of textures, from solid massive silica, brecciated textures to vuggy silica. Two localities of silicified hydrothermal breccias have been identified. Each breccia contains rounded silica nodules with concentric rings of silica contained in silica groundmass. Disseminated and weathered sulfide minerals (pyrite) are present (Siron and Grady, 2011).Meter-scale quartz veins are exposed throughout the prospect. These veins strike north to northeast and appear coincident with the main structural trend. Their origin is unclear, however, they are rarely mineralized and are thought to have formed during reactivation of old structures during metamorphism. A gossanous barite-galena-silver-(gold) vein, containing highly anomalous gold, is oriented along a northeast-trending structure and is exposed near the 4455 foot summit. An additional galena-silver vein in float was uncovered at the base of the silicified fault to the west and is possibly a genetically related mineralized structure (Siron and Grady, 2011).
|Geologic map unit||(-141.312250091692, 63.7996828867089)|
|Mineral deposit model||Creede epithermal veins? (low-sulfidation epithermal) (Cox and Singer, 1986; model 25b).|
|Mineral deposit model number||25b?|
|Age of mineralization||Mineralization was likely synchronous with faulting and magmatism during Late Cretaceous (70 to 68 Ma), indicated from dated hydrothermal mica (Allan and others, 2015).|
|Alteration of deposit||Alteration at South Pika is mostly along northeast-trending faults and is characterized by pervasive silicification and rare hydrothermal breccias, surrounded by a broader zone of clay alteration of feldspar augen porphyroblasts and matrix feldspar. Surrounding the clay alteration is a narrow zone of sericite alteration where schistose matrix biotite has been replaced by fine-grained muscovite (Siron and Grady, 2011).|
|Workings or exploration||
In the mid-1970s Cities Service Minerals Corporation (Cities Services) conducted regional reconnaissance exploration in the Tanacross quadrangle area. Several soil samples and rock samples were collected over the South Pika prospect area at this time (Hedderly-Smith, 2009). This prospect was examined as a porphyry copper deposit at that time, but no significant grades of copper were found (J.M. Messing, oral communication, 1998).
In 1978, one shallow drill hole was put in, but did not encounter significant mineralization. In the late 1980s to 1990s, soil and rock-chip sampling, geologic mapping, and a ground-based magnetometer survey were conducted (Curt Freeman, unpublished data, 1998).
In 2008 Full Metal Minerals (FMM), in a joint venture with BHP Billington, conducted follow-up ridge and spur soil sampling on historic Cities Services data and completed a 31,000 line-kilometer high-resolution airborne magnetic survey covering 1.05 million hectares of the Tanacross quadrangle encompassing the South Pika prospect. The survey shows a moderately high susceptibility anomaly bordering the edge of coincident anomalous gold-in-soil anomaly at South Pika (Siron and Grady, 2011).FMM completed more reconnaissance-style soil and rock sampling and geologic mapping in 2010 which was followed by gridded soil sampling, targeting anomalous gold mineralization. A total of 625 soil samples and 77 rock samples were collected over South Pika. Additionally, four trenches were dug totaling 99 bulk-rock samples. Soil samples from the saddle at South Pika range between trace and 1.09 parts per million (ppm) gold, averaging 0.108 ppm gold. Overall, the characteristic of this soil anomaly exhibits subdued pathfinder element distributions, however, elevated signatures are evident (arsenic: up to 151 ppm; copper: up to 492 ppm; molybdenum: up to 40 ppm; lead: up to 2310 ppm). The northeast-trending barite-galena-silver-(gold) vein near hill 4455 carries upwards of 1.01 ppm gold and 52.1 ppm silver in rock samples and anomalous gold-in-soil over this vein is approximately 100 meters wide and traceable over 1,600 meters along strike (Siron and Grady, 2011).
|Indication of production||None|
|Reporters||C.E. Cameron (ADGGS), N.V. King (Alaska Earth Sciences)|
|Last report date||3/15/2016|