Summary:
Deposit Type
Hundreds of gold occurrences in the southeast USA are located along a 700 km long SW-NE trend that extends from Alabama to Virginia (McCauley and Butler, 1966, Butler and Secor, 1991). Most of these deposits are small prospects worked and explored along narrow quartz veins. The larger gold deposits are located at or near the contact between volcanic and sedimentary rocks, including the Haile, Brewer, Barite Hill and Ridgeway mines. Brewer is unique in the region and is classified as a high-sulfidation epithermal gold system with volcanic and breccia-hosted gold accompanied by quartz, pyrite, topaz, enargite and chalcopyrite. Gold mineralization at Barite Hill contains the assemblage of pyrite-chalcopyrite-galena-sphalerite and is characteristic of a submarine, high-sulfidation volcanogenic massive sulfide deposit. Haile and Ridgeway are similar in that gold mineralization is hosted by silicified, sheared and foliated siltstone.
Mineralization
Economic mineralization at Horseshoe extends below and outside of the pit extents. Mineralization is concentrated in two main zones based on vertical position which form a “horseshoe” geometry over a vertical distance of 350 m. Both zones strike NE adjacent to the siltstone-dacite contact, however, the upper zone dips about 400NW and the lower zone is near-vertical. The upper zone NW-dipping high-grade lenses of mineralization are focused along bedding-parallel foliation with intense silicification. The Horseshoe fault (NE strike, 40NW dip) juxtaposes the hanging wall of upper Horseshoe against barren dacite with a sill-like geometry. This geometry extends southwestward into the nearby Snake pit. The steeply dipping Lower Zone is adjacent to the sub-vertical contact with barren dacite.
Palomino is approximately 650 m southwest of the Horseshoe deposit at 300 m to 500 m below the surface. Deposit dimensions are approximately 300 m long x 50 m to 100 m thick x 100 m to 150 m wide. Lozenge-shaped mineralized zones strike ENE, dip northwest, and plunge gently northeast. Fine-grained gold is hosted in pyritic and silicified siltstone and instrusives, along a steeply SE-dipping, ENE-striking contact with dacite flows. Mineralization is truncated by several NNW-striking, sub-vertical 1 m to 25 m thick diabase dikes. In 2017, a drill program was undertaken at Palomino showing good grade continuity. At the end of 2019, an initial Inferred resource as declared with subsequent drill programs focusing on infill drilling and conversion of Inferred material to Indicated.
Haile gold mineralization occurs as en echelon clusters of moderately to steeply dipping ore lenses within a 4 km x 1 km area.
Orebody geometry, depth, size, grade, mineralogy, and alteration are variable. The orientation of gold mineralization generally parallels the regional NW dipping foliation but is concentrated along the metavolcanic-metasediment contact. Orebody geometry is partly controlled by orientation of volcanicsediment contacts and location of barren dacite sills. Ore lenses are typically 50 to 300 m long, 20 to 100 m wide, and 5 to 30 m thick. Ore zones are separated by barren siltstone, dacite sills and diabase dikes. The Mv/Ms contact and gold mineralization gradually deepen from west to east across the Haile district. The Mv/Ms contact at Champion has been partly removed by erosion in the west portion of the district and is over 500 m deep at the Horseshoe deposit, 4 km east of Champion. Depth and position of the contact are complicated by faulting and folding. Drilling in southeast areas around Palomino has encountered gold mineralization up to 1 km deep.
Gold mineralization at Haile is hosted by laminated siltstone and felsic volcanics in the Upper Persimmon Fork Formation and is capped by less permeable coherent dacite flows. Mineralization is typically within 100 m of the dacite-siltstone contacts. Gold mineralization is disseminated in silicified, pyritic rocks with local K-feldspar and molybdenite. Gold grades in mineralized dacite are typically weaker than in the underlying rocks and sericite alteration is stronger in the dacite.
Mineral zonation grades outward from quartz-pyrite ± K-feldspar + gold (QS) quartz-sericite-pyrite ± gold (QSP) sericite + pyrite ± pyrrhotite chlorite-calcite ± epidote (propylitic). QS and QSP mineralized zones are tens of meters thick. Sericite envelopes range in thickness from tens to hundreds of meters and are controlled by protolith, permeability, and weathering. Within the mineralized zones, quartz is dominant (60% to 80%), pyrite is moderate (1% to 10%), and sericite is variable at 5% to 40%.
Early pervasive, replacement style sulfidation and silicification is overprinted locally by hydrothermal brecciation, quartz stockwork veining, and cm-scale quartz-pyrite veining. These secondary features generally define the high-grade zones within an ore body. Pyritized and sericitized envelopes extend beyond the silicified ore zones, are elongated parallel to foliation, and broadly define the 0.1 g/t Au shell. Pyrite grain size is typically less than 20 microns in ore zones. A late phase of barren, coarse, cubic, undeformed pyrite that formed during regional greenschist metamorphism is present outside of mineralized zones. Pyrite cubes in chloritic metamorphosed rocks are 0.5 to 1 mm in size but can be as large as 1 to 2 cm. Pyrrhotite commonly occurs in 5 to 25 m thick halos around and on the edges of ore zones but is sometimes present within the deeper, underground deposits. Its ductile nature produces length: width ratios more than 5:1 in foliated rocks. Pyrrhotite formation is interpreted to be coeval with early, fine-grained pyrite precipitation.
Supergene sericite-kaolinite alteration forms large bleached, cream to white halos around the ore zones with little to no pyrite that was removed during intense acidic leaching. Strong supergene alteration caps and flanks most of the district. Strong surface alteration is rarely observed deeper than 40 to 50 m. Numerous shallow sericite-kaolinite bodies were mined historically for paint filler.
Propylitic alteration is characterized by increased chlorite (25% to 50%) and a mottled texture with blebs of 1 to 5 mm calcite/ankerite aggregates (2% to 10%) and stockwork. Late quartz ± calcite veining is often focused along fault zones and along shear zones within strongly deformed rocks. Sigmoidal pods of strained quartz are often observed. Oxidation at Haile extends to depths of 20 to 60 m and is deepest along faults and in volcanic rocks. Hematite and goethite are strongest near surface in the saprolite and decrease at depth as weak joint stains.
Gold spatially correlates with silver, arsenic, molybdenum, and tellurium. Base metals are rare at Haile. Thin section petrography and scanning electron microscopy show that the gold occurs as native gold, gold-pyrite and gold-pyrite-pyrrhotite clusters in fine-grained silicified zones. Smeared molybdenite occurs primarily on foliation surfaces and as fine-grained aggregates in silicified zones. Molybdenite at Haile has been dated by Re-Os isotopes at 553.8 ± 9 Ma (Stein et al., 1997), which is coeval with the zircon crystallization age of 553 ± 2 Ma reported by Ayuso et al. (2005). This age correlation indicates that molybdenite mineralization was concurrent with Persimmon Fork volcanism. Seven ReOs molybdenite ages from Haile (Mobley et al., 2014) yielded ages ranging from 529 to 564 Ma. Four of these samples produced an average age date of 548.7 ± 2 Ma (Mobley et al., 2014).