Summary:
Mineralization at McCoy-Cove consists of two mineralization styles, Carlin-style and polymetallic sheeted veins. The Carlin-style mineralization within the Helen, Gap, and Cove South Deep (CSD) zones comprises approximately 85% of the existing resource with high gold and silver grades occurring as both stratabound and structurally controlled mineralization at the intersection of the Cove anticline and favorable lithologic beds, structures, intrusive dikes and sills.
The polymetallic 2201 zone is a separate deposit from the shallower Carlin-style mineralization and is believed to be a structurally controlled sheeted vein system. Veining is oriented northwest, with vein geometry being controlled by a deeper northwest striking reverse fault. Due to its depth, the 2201 zone has seen limited drilling since its original discovery in late 2013, however, additional infill and step-out drilling in the future will help to better define deposit potential and mineralization controls.
Geology
The McCoy-Cove Project is located in the central Nevada portion of the Basin and Range Province, which underwent regional extension during the Tertiary that created the present pattern of alternating largely fault bounded ranges separated by alluvial filled valleys. Prior to this extension, central Nevada had been the site of numerous tectonic events, including at least two periods of regional compression. The property lies west of the central part of the Battle MountainEureka Trend.
The Cove Project contains four structurally controlled mineralized zones within the Triassic sedimentary package. The Helen and Gap zones are Carlin Style disseminated refractory gold deposits. The Cove South Deep (CSD) gold and silver mineralization is associated with disseminated sulfides and is characterized by Ag:Au ratios of 50:1 to over 100:1. The 2201 zone is comprised of disseminated sulfides within sheeted stockwork veins with high concentrations of lead and zinc.
Mineralization
There are four distinct mineralization types known on the property: Carlin-style, polymetallic sheeted veins, carbonate replacement (Manto) and skarn. The Helen, Gap and CSD deposits are Carlin-style deposits while the 2201 zone is comprised of steeply dipping polymetallic sheeted veins.
Carlin-Style (Au-Ag)
The gold in Carlin-style deposits is usually sub-micron in size and generally occurs in pyrite and arsenical pyrite. An envelope characterized by decalcification, silicification, and argillization accompanied by anomalous amounts of silver, arsenic, antimony, thallium, and mercury often accompanies mineralization. The Carlin-style mineralization at Cove is relatively rich in silver compared to similar deposits elsewhere in northern Nevada (Johnston, 2003). When Carlin-style mineralization occurs in the silty limestones and packstones of the Favret Formation and Home Station Dolomite, decarbonatization replaces fine-grained calcite and/or dolomite with quartz and forms very fine-grained illite and pyrite. Diagenetic pyrite was probably present in the Helen Zone before Carlin-style mineralization based on the abundant presence of subhedral pyrite grains that bear no arsenian rims. The arsenic-bearing pyrite precipitated as a product of Carlin-style mineralization in the Helen are fine-grained (~10 microns) patchy, anhedral “fuzzy” pyrite generally smaller than the diagenetic pyrite grains. In the CSD zone, most pyrite grains in high-grade samples are larger (~20 microns), display spectacular, sharp geochemical zonations, and are rimmed with arsenian pyrite or stoichiometric arsenopyrite. The few samples studied from the Gap under the SEM suggest it shares more in common with the CSD zone though its silver content is lower overall.
Polymetallic sheeted veins (Au-Ag±Pb-Zn)
The polymetallic veins in the 2201 zone are enveloped by a zone of illitization of the conglomerate matrix detected by sodium cobaltinitrite staining and confirmed by scanning electron microscope (SEM) analysis. Minor silicification is relatively common, especially in the conglomerate, however, it is not present everywhere and not always directly associated with mineralization.
Carbonate replacement (Ag-Pb-Zn±Au)
Carbonate replacement mineralization occurs as local pods of manto-style mineralization characterized by massive sulfide (pyrite-sphalerite-galena) replacing basal limestone at the Dixie Valley/Favret contact. Mineralization is discontinuous and generally defined by high-grade Ag-Zn-Pb±Au.
Skarn (Au-Ag±Cu): Skarn mineralization at the historic McCoy pit occurs as both endoskarn and exoskarn mineralization characterized by a predominantly garnet-diopside-magnetite mineral assemblage.
The Carlin-style mineralization across the deposit appears to represent an evolving system from a “primary” endmember represented by the CSD zone with higher Ag/Au, coarser-grained pyrite, and a close proximal relationship to Ag-Pb-Zn-(Au) mineralization to the “evolved” endmember represented by the Helen Zone with lower Ag/Au, very fine-grained pyrite, and weak spatial association with any other styles of mineralization. The Gap can be considered a “transition” zone between the two endmembers until more petrography is conducted on the recently discovered Gap to test this hypothesis. Helen Zone geochemistry is distinct from the CSD zone in many ways.
Like the geochemistry, the mineralization in the Helen and CSD is also distinct. The As-bearing (assumed to also be Au-bearing) pyrite in the Helen are generally finer-grained, less euhedral, and more poorly zoned than the As-bearing CSD zone pyrite. Helen pyrite overall has lower As content, ranging from just at detection limit (~0.3 wt% to 0.5 wt%) to 2.1 wt%, than the CSD zone which contains pyrite with arsenic contents ranging from detection limit to 6 wt%. The SEM-EDS system first detected trace elements such as Te, Tl, Hg, Sb, and even Au and Ag in CSD zone pyrite, while electron microprobe analysis confirmed the presence of Au, Ag, As, Tl, Hg, Sb, and Pb in CSD mineralization. Other pyrite in the CSD zone contain fewer trace elements but still display complex elemental zoning and growth patterns visible only in backscatter electron imaging. The complicated nature of the mineralized pyrite at the CSD zone is suggestive of a more complex and long-lasting mineralizing event in comparison to the seemingly simple Helen mineralization.
In the 2201 zone, Au correlates with Ag, As, Cu, Fe, Pb, Sb, and Zn – a distinctly different grouping of elements from the CSD, Gap, and Helen Zones. The 2201 zone veins typically occur as sheeted veins and range in thickness from 0.1 cm to 6.5 cm and contain both quartz and carbonate minerals as gangue. Generally, the calcite and dolomite-dominant veins are shallower and thinner whereas the quartz (-carbonate)-bearing veins are deeper and can reach widths of 15 cm. The sulfides are mostly pyrite, sphalerite, and galena with arsenopyrite, chalcopyrite, and pyrrhotite also locally present. Visible gold is mostly limited to the thicker veins and is always observed along the margins with coarse-grained quartz. When microscopic, the gold is present as electrum with approximately 15 wt% Ag (measured on SEM-EDS) and hosted within sulfides such as chalcopyrite or arsenopyrite. Galena may also carry up to 10 wt% Ag. There were no trends for veins grouped by gangue or thickness, however, when grouped by depth, the data show that veins shallower than 1,750 feet generally strike northeast-southwest with varying dips and veins deeper than 1,900 feet generally strike northwest-southeast and dip steeply in both directions.