Summary:
The Moss deposit is a steeply dipping (average 70°) quartz-calcite vein and stockwork system, which extends over a strike length of approximately one mile in the resource area (Moss Open Pit and West Pit), but can be traced for 3.9 miles in total length.
The Moss Vein system is considered a high level, low-sulfidation (adularia-sericite) epithermal gold-silver deposit in the classification of Heald et al (1987) and White and Hedenquist (1995). Low sulfidation epithermal deposits form from hydrothermal waters in the relatively near-surface environment, typically within 1.5 km of the earth’s surface (Taylor, 2007). They are commonly found associated with magmatism and volcanism, but are somewhat distal (vertically or laterally) from the actual center of magmatism, in environments where meteoric waters have mixed with and diluted magmatic waters.
The quartz-calcite vein textures at Moss (massive, breccia, vuggy, colloform), are typical of low sulfidation epithermal veins. Gold occurs as very fine native gold and electrum, and silver typically occurs as electrum and very fine grained acanthite, similar to other lowsulfidation precious metals deposits.
The very low (usually trace) levels of base metals in the Moss ores are also consistent with high-level low-sulfidation gold deposits. Alteration related to main-stage precious metals mineralization is confined to silicification and minor sericitization of wall rock adjacent to the veins.
The Moss mineralization differs from typical low-sulfidation precious metals deposits in its lack of adularia (possibly present, but not yet positively identified) and lack of deleterious elements such as arsenic, antimony, and mercury.
The high level of emplacement of the Moss mineralization is evidenced by the very fine grain size of ore-stage minerals (gold, silver, electrum, acanthite) and the highly vuggy nature of much of the vein. No paleosurface or near surface features, such as silica sinters, chalcedony or a steam-heated acid leach cap, are preserved in the Moss project area. This indicates that the top of the hydrothermal system has been eroded, thereby exposing the gold depositional zone. Larson (2015) notes that much of the quartz in the Moss Vein was likely deposited as chalcedony or opal, which later converted to fine-grained quartz. This would place the upper part of the Moss Vein system only slightly below the surficial hot-spring zone.
Mineralization
Gold-silver mineralization in the West Oatman district occurs as high-level low-sulfidation epithermal veins and stockworks. The mineralization is very similar to that of the main Oatman mining district. The Moss Vein may represent the western extension of the Gold Road vein on the north end of the Oatman district.
Three main veins and their associated stockworks host the bulk of mineralization defined to date at Moss: 1) the Moss Vein and its extensions to the west and east of the resource area; 2) the Ruth Vein to the immediate south of the Moss Vein, and 3) the West Oatman Vein, lying about one mile to the south of the Moss Vein.
Moss Vein System
The Moss Vein system extends for 3.90 miles in a roughly east-west direction across the Moss/Silver Creek claim block. The vein has been divided into three sections for exploration and mining purposes:
• the Main Moss Vein/resource area (Moss Open Pit, West Pit), comprising 1.2 miles of the Moss vein on the patented mining claims
• the Eastern Extension, extending for. 1.5 miles eastward from the east end of the open pit to the east end of the Silver Creek claims where the vein intersects the NNWtrending Mossback Vein
• the Western Extension of the Moss Vein, extending for 1.20 miles from the west end of the West Pit to the Far West prospect., including the Cliffs of Mordor/Mordor Vein and the Mid-West target.
In the central part of resource area, within the Moss Open Pit, the Moss Vein strikes eastsoutheast (~96º azimuth) and dips steeply (~70o ) to the south. The Ruth Vein and other small veins in the hanging wall of the Moss vein are antithetic veins dipping to the north.
Geological mapping combined with review of Moss Mine Project drill hole logs and assay database indicate the potential for exploitation of other mineralized veins and stockwork zones between the Moss and Ruth Veins.
West Extension of Moss Vein
The Moss vein can be followed for 1.20 miles west of the West Pit, and is expressed on surface as quartz+/-calcite veining, stockwork veining, or silicification along trend of the vein. Four mineralized areas within the West Extension are discussed separately: West Pit, Mordor, Mid-West Extension, and Far West.
West Pit
The West Pit mineralization is part of the main Moss Vein/resource area. Strong gold-silver mineralization follows the Moss Vein to the west across the Canyon fault, a major north-northwest linear. The structure of the Moss vein crosses the Canyon fault apparently without change in orientation, and although it appears as if there is little displacement across the fault, potential movement along the fault is being tested with additional drilling. Movement along the Canyon fault may pre-date the Moss vein; drill testing will confirm whether post-mineral movement is minor.
Cliffs of Mordor/Mordor vein
The rugged cliff terrain west of the topographic crest of the West Pit is informally named the Cliffs of Mordor. Stockwork and vein mineralization continues west of the pit, but has until recently been difficult to access and drill due to the rugged topography. Pioneering in the West Pit has created the opportunity for drilling from various flat benches within the pit as it develops. The host rock changes from the Moss porphyry to welded tuffs of the Peach Springs tuff west of the West Pit boundary. The tuffs are competent host rocks capable of propagating both veins and stockwork mineralization, as manifest in the presence of numerous veins in outcrop to the west of the current mine. A well-defined quartz-calcite vein, the Mordor vein, crops out along the base of the cliffs, just west of the leach pads. The vein strikes 260° and dips 50° to the north in outcrop and can be followed for about 400 feet along strike. Continuous-chip samples collected across the 5- feet-width of the vein ranged from 0.079 oz/ton to 0.286 oz/ton Au.
Mid-West Extension
To the west of the Cliffs of Mordor, about 1,800-2,300 feet west of the West Pit, the Moss Vein crops out as a rib of replacement silicification with minor white quartz veining for about 1,000 feet of strike length. Several prospect pits and one short adit are remnants of historic exploration of the vein.
Far West
The Far West extension of the Moss Vein comprises the westernmost exposures of the vein system. Following a gap of about 1,500 feet lacking surface expression of the Moss Vein, the structure reappears as a broad zone of stockwork veining with quartz-calcite+/-fluorite veins extending for about 2,000 feet along the steep south flank of a large hill (the Black Fin).
Ruth Vein
The Ruth Vein is an epithermal quartz-calcite vein, similar and subparallel to the Moss Vein, lying about 650 feet to the south of Moss in the central area and dipping about 60 degrees north toward the Moss vein. The vein crops out as a four to six-foot-wide solid quartz+/-calcite vein, extending from the shaft at the old mill site near the present mine office to two shafts lying about 600 feet to the east. The shafts serviced workings developed in a high-grade (~0.35 oz/ton Au, 2.0 oz/ton Ag) ore shoot that raked about 45 degrees to the east. The main productive area of the Ruth Vein strikes nearly east-west and dips north at 50-70 degrees (267/50-70). The east and west extensions have more northeasterly trends with an orientation of approximately 255/65.