13 Economic Geology/Geochemistry/Mineralogy (Posters)

Thursday, 24 March 2011
1:30 PM - 5:30 PM
Exhibit Hall

LITHOLOGICAL VARIATIONS AND CALCITE TWIN GEOMETRY TEMPERATURE RANGES IN THE KINDLEY MINE, ASHEBORO, NORTH CAROLINA

Paper number: 13-12
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

During the mid-1980’s, the Phelps-Dodge Corporation prospected the Uhwarrie Mountain region of south-central North Carolina in search of gold. Five NX core were drilled at the Kindley Mine in the northeast quarter of the Denton Quadrangle, Randolph County near Asheboro. Core PDKY-5 was drilled vertically 425’ and penetrates two lithologic units. The upper 247’ is Uhwarrie Formation felsic crystal tuff with a mineral assemblage of quartz + calcite ± epidote ± plagioclase ± chalcopyrite ± pyrite ± dolomite. Below 247’, the lithology changes to a 45-foot zone of interfingered felsic crystal tuff and laminated mudstone. The laminated mudstone (from 292’ to 402’ depth) represents a turbidite succession of the Tillery Formation with a mineral assemblage of very fine-grained quartz + opaques and trace amounts of calcite. Calcite is restricted to fracture-fill throughout the mudstone; one sample from 338’ had 63 modal percent. The mudstone encounters a more lithic crystal tuff at ~402’. The contact at this depth also displayed an interfingering orientation of the mudstone and tuff for ~10 feet.

Twinned calcite, found as vein- or fracture-fill, is associated with disseminated sulfide mineralization in both lithologies. Alizarin-red and potassium ferrocyanide blue staining techniques on slabs and thin sections indicates carbonate ranging from 30 to 40 modal percent within the top 200’ of the core. The tuff below the mudstone contains a greater abundance of calcite as both vein- and fracture-fill. The calcite twin geometry (termed “intensity”) can be used to suggest deformation temperatures using the method of Ferrill et. al. (1991). Types 1 and 2 twins (150-300° C) occur most abundantly at shallow depths, but are found throughout the core. Types 3 and 4 twins (>200° C) are generally found below 200’ in the tuff and these temperature relationships provide new information on the deformation events that have occurred in these rocks.