The Snow Camp-Saxapahaw study area, in the Carolina
slate belt in the Southeastern United States, is notable for large zones
of high-sulfidation alteration in arc-related metavolcanic rocks. The
area has potential for additional significant pyrophyllite and related
aluminosilicate refractory mineral deposits and may have potential for
small- to medium-size gold deposits also associated with the high-sulfidation
The Carolina slate belt is an elongate zone of mostly low-grade metamorphic
rocks of Neoproterozoic to early Paleozoic age that extends from northeastern
Georgia to southern Virginia. It is dominated by volcanic rocks but locally
consists of fine-grained epiclastic sedimentary rocks. Plutons and subvolcanic
bodies have intruded the rocks of the Carolina slate belt in many places
and have been important in controlling the metamorphism and in localizing
The Snow Camp-Saxapahaw area is mostly underlain by volcanic and volcaniclastic
rocks and lesser amounts of intrusive shallow plutons. The volcanic rocks
range in composition from basalt to rhyolite; however andesites, dacites,
and rhyodacites are the most abundant. The intrusive bodies are largely
granite and quartz monzonite; gabbroic bodies also are common. It was
possible to establish the relative ages of only part of these rocks.
Two northeast-trending fault zones and fractures divide the map area
into three structural blocks; the central block was tilted down to the
southwest to form a grabenlike structure. Most of the hydrothermally
altered rocks and all of the intensely altered zones are confined to
the downdropped block, which we think may have been calderalike in origin.
A major volcanic unit, the Reedy Branch Tuff, is limited to the southwestern
part of the graben and may be the youngest volcanic rock in the area.
Layered rocks record one or more strong folding events, but the diversity
of rock types, lack of recognizable stratigraphic markers, and uneven
distribution of outcrops prevented comprehensive structural studies.
Except for a few late plutons and dikes, all of the rocks of the area
have been metamorphosed in middle to upper greenschist facies, and contact
aureoles were recognized around some of the plutons. Several relatively
small bodies of granitic rock contain plagioclase grains in which primary
oscillatory zoning was unaffected by metamorphism. These were interpreted
to be post-metamorphic.
We think that there were three separate stages of hydrothermal alteration
in the complex volcanic terrane in the area. The oldest, an area of at
least 8.5 square miles (22 square kilometers), was subjected to an intense
hydrothermal alteration, ranging from peripheral zones of quartz-sericite-paragonite
through a patchy marginal zone of pyrophyllite, andalusite, and other
high-alumina minerals, to almost totally silicified core zones. The second
event resulted in large areas of weak to moderate sericitic and propylitic
alteration recognizable only in the Reedy Branch Tuff. The last event
was related to post-metamorphic plutons.
All of the pyrophyllite-andalusite deposits and perhaps most of the
gold and silver mineralization can be related to the first period of
hydrothermal alteration. The subsequent metamorphism did not produce
significant changes in mineral species in the zones of most intense hydrothermal
alteration. Gold- and silver-bearing sulfide minerals in fracture zones
along the southeastern margin of the graben may also have been deposited
during this earliest alteration stage. No metallic mineralization appears
to have occurred during the second event. A group of molybdenum-bearing
greisenlike bodies formed during the emplacement of the youngest plutons
during the post-metamorphic event. One gold-bearing sulfide zone occurs
in the exocontact of one such porphyritic stock.
Significant amounts of pyrophyllite-andalusite-bearing rock have been
extracted from the Snow Camp Mine and from several smaller pits. There
may be other undiscovered deposits in this area. Small gold mines were
operated here in the nineteenth century and probably in the early decades
of the twentieth century, but we found records of production and descriptions
in the geologic literature of only smaller prospects. No mines were being
operated here during our study. There may be other exploitable deposits
near and in the siliceous core zones of intense high-sulfidation alteration
and in fracture zones along the southeastern side of the graben structure.
Evaluation of the gold potential was based on the results of stream-sediment
sampling, on the analyses of sulfide-bearing rock from shear zones, on
the mining history of the area, and on comparisons with districts having