THE RIDGEWAY GOLD DEPOSITS, SC: SOME OLD AND NEW IDEAS REGARDING POSSIBLE ORIGINS FOR THESE FOSSIL HYDROTHERMAL GOLD DEPOSITS

Rio Tinto’s Kennecott Ridgeway Gold Mine (KRGM), located in the Carolina Terrane (CT) of South Carolina, operated from Dec. 1988 through Nov.1999. The KRGM mined low grade disseminated gold ore from the North and South pits, located 1 mile apart, and poured 1.44mm oz of Au and 850k oz of Ag.

The KRGM Au deposits are complexly deformed, and ore deposit models proposed over the past 33 years include exhalative, epithermal, synmetamorphic shear zone, and a hybrid of the three. More recently, metavolcanic ages of ~556ma, comparable ages of molybdenite mineralization, S isotope work, and ore microscopy studies have provided compelling arguments that syngenetic-exhalative and/or epithermal replacement systems were very important in the creation of these deposits.

Thus, where do tectonism and metamorphism figure into the genesis of the KRGM deposits? The highest grades of Au are typically associated with texturally complex alteration zones (fragmented, sheared, transposed) oriented parallel to a regional, lower greenschist facies slatey cleavage, which regionally dips north (N pit cleavage was later warped into an upright synform). The cleavage-parallel alteration zones also typically cross cut bedding in the host metasediments and metavolcanics. Numerous other Au deposits in the region also show these relationships leading some to conclude the Au deposits were formed during a later, ~450ma? diachronous metamorphic event that was coincident with formation of a shear zone. This talk will show field and microscopy evidence that support an alternative interpretation - that the cross cutting alteration zones are the former, fault-controlled hydrothermal feeder zones for these systems and that they were later modified during metamorphism.