SILVER SHAFT MINE VMS MINERALIZATION AND HYDROTHERMAL ALTERATION: PETROGRAPHIC EXAMPLES FROM CORE HOLE PDSS-3, ROWAN AND CABARRUS COUNTIES, NORTH CAROLINA

Core hole PDSS-3 intersected late Proterozoic VMS mineralization of the Silver Shaft (McMakin) Mine deposit in the Gold Hill District. A drill hole cross section with assays is presented, along with core photographs and petrographic studies of the mineralization and hydrothermal alteration.

From the surface to 574-foot total drilled depth the hole cored: 0-52 feet (overburden); 52-314 feet (massive to poorly bedded siltstone, that is locally siliceous to fragmented with a trace to 5% disseminated pyrite); 314-404 feet (massive to well bedded mudstone that is locally silty, siliceous or talcose with 3-5% pyrite and locally up to 20-30% pyrite); 404-445 feet (talc and talc-carbonate mineralization that is locally brecciated with 1-5% disseminated pyrite as grains and laminae, trace to 5% sphalerite, and trace to 1% aguilarite); 445-463 feet (mudstone, locally silty, siliceous or talcose containing 1-3% pyrite, and trace sphalerite and aguilarite); 463-574 feet (massive to poorly bedded siltstone, locally siliceous to fragmented with a trace to 3% pyrite).

The mineralized horizon’s primary mineral assemblage is talc+carbonate+sulfides+barite. The primary ore minerals are pale-colored low-Fe sphalerite and a silver sulfide identified as aguilarite. Primary pyrite is preserved as individual framboids and laminae that may be stretched, micro-folded and dismembered by shearing. Spongy pyrite cores representing vestiges of primary (?) mineralization are surrounded by metamorphic (recrystallized) poikiloblastic pyrite metacrysts with clean rims. Disseminated pyrite is strung along the tectono-metamorphic fabric with very strong foliation and likely shearing and sphalerite and galena are strongly remobilized. Possible banded and crustiform carbonate features enclose small amounts of barite and represent a portion of the primary “sulfide mound” textures formed in channel ways.

The metamudstone fabric is strongly foliated, sheared, transported and recrystallized. It is overgrown by poikiloblastic pyrite metacrysts with spongy cores. Minute amounts of sphalerite were emplaced along fractures in the pyrite.