|Moss and Mossback mines, San Francisco (Oatman) district, Arizona showing locations of |
anomalies (yellow pins) and lineaments (red lines). Google Earth
The Moss lies 2-miles, on-trend, west of the Mossback mine (inactive), 5.5 miles northwest of the Gold Road mine (active), 11 miles southeast of the Katherine gold mine in the Union Pass district, and is the northernmost extent of known gold mineralization in the San Francisco district of the Black Mountains. Nearby towns include Bullhead City (6-miles west), and Oatman (6-miles southeast).
The vein is hosted by Tertiary, Moss quartz monzonite porphyry (Gardner, 1936; Noland, 2010), with the structure being open along strike and at depth. In the past, shafts were sunk 100- and 230-feet deep with 1,700-feet of drifts. A calcite-quartz stockworks vein occupies the hanging wall of a high-angle fault and is overlain by as much as 100-feet of low-grade, mineralized, stockworks and siliceous breccia classified as low-sulfide, adularia-sericite, epithermal vein typical of many near surface, hydrothermal systems. Such deposits are often related to paleo-hot springs and/or shallow geothermal systems. The vein has some fluorite (Lausen, 1931).
Along the southern portion of the vein, a group of conjugate veins occur in the hanging wall that have a similar trend, but dip northerly. Much of the historical gold and silver production from the vein was from conjugate veins.
In the 1980s, Harrison Mining dewatered the shaft and mined 3,000 to 5,000 tons of ore that averaged 0.29 opt Au. In 2004, Patriot Gold Corporation optioned the property and identified auriferous veins unrelated to the primary vein that include the Discovery and Ruth veins. In 2009, Northern Vertex picked up the property and drilled more than 670 holes (Preston, 2013).
Using a 0.01 opt cutoff grade, the Northern Miner reported the deposit has 22.6 million measured and indicated tonnes grading 0.023 opt Au and 0.26 opt Ag, plus 3.9 million inferred tonnes averaging 0.017 opt Au and 0.2 opt Ag. In total, known resources include 603,000 ounces of gold and 6.6 million ounces of silver within 650 feet of the surface (Preston, 2013, Wilson and Redwood, 2012).
Holes drilled in the western extension of the vein were designed to test near surface quartz-carbonate stockworks open to the south. Multiple zones of stockworks veining (randomly oriented veins and veinlets, sometimes referred to as stinger zones) encountered within 500 feet of the surface, suggest potential for widespread mineralization to continue south. Eight additional drill holes demonstrate strong development of quartz-carbonate veins, breccia and stockworks that continue from the surface to at least 650 feet deep.
An airborne magnetic survey by Patriot Gold indicates the Moss structure is a well-defined, magnetic high. The survey identified 1.8-miles of unexplored magnetic structure, and also identified nine linear structures associated with known mineralization, and one 3.6 mile structure was likely an extension of the Gold Road deposit. Recently, a heap leach pad was constructed south of the Moss vein (35°5'43"N; 114°26’55"W) presumably to extract gold from low-grade ore. Northern Vertex poured its first gold bar in early 2018.
At the eastern extent of the mineralized zone, the Mossback mine lies along the edge of Mossback Wash. The property was claimed in 1863 and a shaft sunk to a depth of 800 feet. The vein is in andesite and as much as 90-feet wide with an 80o dip. Vein-filling consists of brecciated andesite and calcite with subordinate amounts of quartz, with spotty ore. In addition, the area appears to have an extensive gossan based on aerial photography (Hausel, 2020).
Recently, Elevation Gold Gold Mining Company published mineral resource estimates of gold and silver for the Moss mine as of December 2019. They report measured, indicated and inferred resources totaling 489,000 ounces of gold and 5, 838,000 ounces of silver.
The operation features a an open pit. The ore is crushed, agglomerated and heap leached followed by processing in a metal recovery plant and refinery, with a final process of production of gold and silver doré bars.
"The resource estimate update found that from the start of operations to December 31, 2019, mining operations depleted approximately 71,000 ounces of gold, however with drilling success, these mined ounces have been more than offset by an addition of 86,000 ounces of gold in the inferred category. In comparing the updated December 31, 2019 resource estimate to the resource estimate in the Technical Report, aggregate measured and indicated gold ounces fell by approximately 8% primarily due to depletion from mining activities, while inferred gold ounces grew by almost 300% due to the identification of new resources from infill drilling. Exploration upside potential at Moss is excellent as the deposit continues to remain open for resource expansion along strike (at both ends) and at depth".