Summary:
Haile is situated within the northeast-trending Carolina Terrane, also known as the Carolina Slate Belt, which hosts the past-producing Ridgeway, Brewer and Barite Hill gold mines in South Carolina. Haile is the largest gold deposit in the eastern USA. The Haile district consists of nine gold deposits within a 3.5 km x 1 km area. The deposits occur within a variably deformed ENE-trending structural zone at or near the contact between metamorphosed Neoproterozoic volcanic and sedimentary rocks. The deposits are hosted in laminated siltstones and volcanic rocks of the Upper Persimmon Fork Formation and are dissected by barren NNW-striking diabase dikes. Deformation includes brittle and ductile styles with ENE-trending foliation, faults, brecciation, and isoclinal folds. Sedimentary rocks are folded within an ENE-trending anticlinorium with a steep SE limb and a gentle NW limb.
Haile is interpreted as a structurally controlled, low-sulfidation, disseminated gold deposit.
Mineralization and Alteration
Haile gold mineralization occurs as en echelon clusters of moderately to steeply dipping ore lenses within a 4 km x 1 km area. Nine named gold deposits are recognized at Haile. From west to east, these deposits include Champion, Small, Mill Zone, Haile, Ledbetter, Red Hill, Palomino, Snake and Horseshoe that often show ‘pearls on a string’ alignment. Ledbetter is by far the largest orebody (approximately 1 Moz) and includes the shallow Chase and deep Mustang deposits. 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 volcanic sediment 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. Small, mineralized zones at Ledbetter, Red Hill, Mill Zone, and Snake are hosted in the overlying dacite along fault zones within 15 m of the Mv/Ms contact. Gold grades in mineralized dacite are typically weaker than in the underlying rocks and sericite alteration is stronger in the dacite. Hydrothermal brecciation is common in portions of the Ledbetter, Horseshoe, Small and Champion deposits where milled, silicified siltstone clasts occur in a fine grained quartz-pyrite matrix intruded by fingers of quartz feldspar porphyry with quartz stockwork veinlets.
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%. Semi-massive pyrite zones are locally observed over thicknesses of 0.5 to 5 m, especially in the Mill Zone, Red Hill and Haile pits.
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 Re Os 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).