Sleeper Mining Company, LLC, which is an indirect wholly-owned direct subsidiary of Paramount Gold Nevada Corp., holds an 100% interest in the Sleeper Gold Project.
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Summary:
The Sleeper gold-silver deposit is located on the western flank of the Slumbering Hills and is largely covered by Quaternary gravels, alluvium, colluvium, and a surficial sequence of eolian sand. Gold-silver mineralization is situated nearly entirely in the hanging wall of a major, northwest-trending, west-dipping range-bounding normal fault that separates Mesozoic metasedimentary rocks of the Auld Lang Syne Group in the footwall from middle Miocene lavas, flow breccia, and lesser epiclastic and tuffaceous rocks in the hanging wall. The principal host rocks for the deposit are a sequence of middle Miocene basalt and rhyolite lavas, domes, and small-volume tuffs.
The deposit is hosted by Tertiary Sleeper Rhyolites and Tertiary Sleeper Basalts. The deposit is comprised of a core zone characterized by the mined-out Sleeper vein that lies within a broad envelope of lower-grade mineralization.
Prior to mining, the Sleeper deposit consisted of four spatially overlapping types of gold-silver mineralization: a) banded quartz-adularia-electrum-(sericite) veins; b) silica-pyrite-marcasite cemented breccias; c) quartz-pyrite-marcasite stockworks; and d) alluvial gold-silver placers in Pliocene gravels.
The Sleeper veins generally dip to the west at moderate to high angles, but some secondary hangingwall offshoots of the principal vein structures dip steeply to the east. Significant zones of mineralization at Sleeper extended for about 1,500 meters along strike, about 600 meters of width, and from near the pre-mining surface to depths of more than 610 meters. At least eleven veins with bonanza grades were mined historically. The Sleeper Main vein produced more than 0.5 Moz of gold from a single bonanza ore shoot, which had a strike length of 850 meters and width ranging from 0.3 to 4.6 meters. Most discrete bonanza zones consisted of a series of sheeted chalcedonic quartz veins distributed over cumulative widths of 10 to 25 meters. Individual veins ranged in thickness from a few centimeters to locally 5 meters.
The post-mining Sleeper deposit is predominantly characterized by extensive, low-grade stockwork mineralization hosted within the Sleeper rhyolite and underlying basalts. The stockwork mineralization has numerous, randomly oriented quartz-pyrite-marcasite veinlets peripheral to mid-to high- grade veins and breccias. The mid-grade mineralization consists of clast-supported breccias and narrow veins which extend down-dip from previously mined high-grade veins. These mid-grade narrow veins typically assay between 3 and 34 g Au/t, whereas the stockwork assays usually result in grades less than 3 g Au/t.
The West Wood area to the southwest of the Sleeper pit contains high-grade mineralization within a hydrothermal breccia body associated with faults and a felsic porphyritic intrusive. This zone likely represents a down-faulted block that was continuous or parallel to the West vein mined in the pit. The West Wood breccia is highly silicified with abundant sulfides, but localized veins within the breccia can exceed 100 g Au/t.
The low-grade mineralization has extents of approximately 2,000 meters east-west, about 1,250 meters north-south, and up to 600 meters in the vertical direction. Sub-horizontal and sub-vertical veins and breccia bodies of the mid- and high-grade mineralization extend outward into the lower-grade envelope, likely due to stratigraphic and structural controls. The base of the Sleeper vein core zone is sharp, marked by a distinct decrease in the precious-metal grades.
High-grade mineralization (>8 g Au/t) within the core zone related to the Sleeper vein and its stratigraphic and structural extensions has been documented to have been most frequently associated with thin (>8 g Au/t) within the core zone related to the Sleeper vein and its stratigraphic and structural extensions has been documented to have been most frequently associated with thin (<5 centimeters), often banded, typically steeply dipping chalcedonic quartz + adularia veins/veinlets. It is important to note that there are examples of high-grade mineralization that have no obvious association with veins, and the presence of veins does not guarantee high grades. In addition, the Sleeper fault has been hypothesized to be the primary controlling feature in the formation of the deposit, and there is evidence of an association between high-angle structural zones and increases in vein density and grades. The distribution of high-grade mineralization distal to the Sleeper vein is somewhat erratic but is locally systematic. For example, the high-grade mineralization at West Wood and the Office areas is related to hydrothermal brecciation.
Stratigraphic control of moderate-grade mineralization is expressed by lenses of generally concordant mineralization that extend outward from the margins of higher-grade mineralization along the hanging wall and footwall of the Sleeper vein.
The Sleeper gold- and silver-bearing hydrothermal fluids are interpreted to have been introduced into the Sleeper Rhyolite and Basalt units along a series of northeast-striking, steeply dipping (primarily to the northwest) structural zones, within the core zone of the deposit. The planar base of this zone and the abrupt change to weakly mineralized and altered rocks below likely reflect the elevation at which boiling of the ascending hydrothermal fluids and deposition of high-grade mineralization was initiated. Outside of the core zone of the Sleeper deposit, deposition of high-grade mineralization is more erratic, which suggests that fluid flow was less focused along poorly defined structural zones. The waning stages of the mineralizing system appear to be manifested as “multi-stage hydrothermal breccias”. These primarily clast-supported breccias contain rotated fragments and some mineralized quartz veinlets. The breccias are cemented primarily by silica, contain pyrite, marcasite and adularia and are almost entirely post-mineral.
Post-mineral faulting has resulted in a slight tilting of the Sleeper deposit and its host stratigraphy to the west.