Summary:
The structural setting, alteration mineralogy and mineralization characteristics of the deposit is consistent with Carlin-type deposits.
Geology
The Property is located on the eastern flank of the Osgood Mountains within the Basin and Range tectonic province of northern Nevada. The geology throughout the Osgood Mountains is typified by folded Cambrian to Ordovician sedimentary rocks that have been intruded by Cretaceous stocks, which have been cross-cut by later high-angle structural deformation. Hotz and Willden (Geology and Mineral Deposits of the Osgood Mountains Quadrangle, Humboldt County, Nevada: U.S. Geological Survey Professional Paper 431, 1964) suggest the high angle faulting is related to the Basin and Range extension. The older rocks are overlain by Miocene andesitic basalt and the surrounding fault bounded basins are filled with quaternary alluvial (Qal) gravel. The Osgood Mountains have a general northeast trend, although, at a structural hinge in the vicinity of the Granite Creek Mine, the east flank of the range rotates and trends north towards the Getchell mine. Gold mineralization is primarily hosted by fine-grained marine sedimentary rocks that overlie a large stock of Cretaceous granodiorite.
Mineralization
Mineralization at Granite Creek is structurally controlled. Faults are the primary control of mineralization, especially in high-grade underground zones. Lithologic contacts, bedding, and folds also play an important role, especially in near surface (open pit) mineralization. High-grade mineralized zones are moderately continuous along faults with the most prolific zones occurring at structural intersections. Gold mineralization is found within pyrite that consists of two stages of development, an early, uneconomic gold-bearing pyrite stage and a gold-bearing arsenian pyrite stage (Ridgley, et al., 2005). Megascopically, the gold-bearing pyrite is typically dull brassy to black in color and very fine-grained. Pyrite may also be associated with remobilized carbon, imparting a “sooty” appearance to the pyrite. Gold is primarily contained in pyrite as microscopic inclusions or found in solid solution within arsenian-pyrite rims around fine pyrite grains ( (Wallace, et al., 1983; Foster, 1994; Ridgley, et al., 2005). Gold mineralization shows a correlation with arsenic, antimony, mercury, and thallium.
Gold mineralization at the Property is primarily hosted by the Upper and Lower Comus Formations, which consist of argillite and interbedded argillite and limestone, respectively. The Upper Comus is the primary host lithology in the Mag Zone and currently is host to the majority of surface resources at the Pinson (Granite Creek) deposit (Gustavson, 2012). The Upper Comus is also locally mineralized within the B, C, CX, CX-West, and portions of the RFZ. The Lower Comus hosts the majority of the high-grade underground resources. In areas proximal to the Osgood Mountains stock including the underground resources, most of the host rock has been metamorphosed. In these areas argillite has been metamorphosed to hornfels with limestone altered to garnet, pyroxene, wollastonite, and marble. Higher gold grades are typically located in these metamorphosed rocks along fault zones due to the lack of wall rock permeability.
Multiple areas of high-grade gold mineralization at the Granite Creek deposit are amenable to
underground mining methods, as shown by previous operators. These include the Rangefront, Otto-Adam
Peak, Ogee CX, and South Pacific Zones. All of these zones show strong structural control.
Rangefront Zone
The RFZ consists of pervasive argillization and decarbonatization with intense brecciation along the lower bounding RFF. Structural/mineralization trends are difficult to discern in this zone with mineralization occurring as discontinuous amorphous bodies within the Comus Formation. High-grade zones are concentrated in the Lower Comus with anomalous mineralization present in the Preble Formation, proximal to the RFF. Silicification is minor, with calcite veins occurring along the margins of fault zones. Structural and dissolution breccias that occur along bedding and structural intersections within the Lower Comus Formation are particularly receptive to mineralization. The zone has a strike length of approximately 950 feet (290 meters), a down dip extent of 1,100 feet (335 meters), and an average width of 100 feet (30 meters).
Otto-Adam Peak Zone
The Otto-Adam Peak zone is defined by the Otto and Adam Peak faults and their associated splays. The zone trends northeast, dips southeast, plunges to east-northeast and is offset down-dip by the CX West fault. The zone is pervasively argillized with intense brecciation occurring along faults. Mineralization is moderately continuous, controlled by a network of discrete anastomosing faults and splays within the Lower Comus Formation. High grade mineralization occurs along fault intersections throughout the zone. The mineralization has a strike length of approximately 500 feet (152 meters), a vertical extent of 700 feet (213 meters), and an average width of 75 feet (23 meters).
Ogee Zone
The Ogee zone is an east-northeast trending near vertical mineralized zone controlled by the Ogee Fault and associated splays. The zone is argillized, decarbonatized, and intensely brecciated along faults. The upper portion, defined by the intersection of the Ogee Fault and the contact between the Upper and Lower Comus Formation, plunges to the east-northeast at 55°. The lower portion is near vertical and controlled by faults and structural intersections. The upper portion is strongly oxidized while the lower portion is mostly oxidized but contains more comingled sulfide. The mineralization has a strike length of 400 feet (122 meters), a vertical extent of 1,500 feet (457 meters), and an average width of 75 feet (23 meters).
CX Zone
The CX zone consists of both near-surface (open pit) and higher-grade underground mineralization. The lower-grade open pit mineralization is controlled by the through-going CX fault and its associated hanging wall and footwall splays. Mineralization is discontinuous and associated with pervasive argillization and decarbonatization within structural and dissolution breccias in the Lower Comus Formation. The near-surface portion of the zone has a strike length of 3,500 feet (1,066 meters), a down-dip extent of 400 feet (122 meters), and an average width of 75 feet (23 meters). The higher-grade underground portion of the mineralization is more tightly structurally controlled along the down-dip section of the CX Fault with an average width of 40 feet (12 meters). The underground portion of the zone has a strike length of 1,000 feet (305 meters) and a down-dip extent of 1,200 feet (366 meters).
South Pacific Zone
The South Pacific Zone (SPZ) is a northeast-trending and southeast-dipping zone of high-grade fault-bound mineralization with a northeast plunge of 45°. The mineralization is controlled by the along-strike and down-dip extent of the Otto fault. The zone is defined by a suite of northeast-striking striking moderately southeast dipping anastomosing fault splays with the highest grades concentrated along faults that juxtapose the Upper and Lower Comus Formations. The mineralization has a strike length of 1,250 feet (381 meters), a down-dip extent of 900 feet (274 meters), and average fault-bound mineralization widths of 25 feet (7.6 meters).