September 13, 2002
WSGS Completes Rattlesnake Hills Geologic Map
Geologists with the Wyoming State Geological Survey (WSGS) recently completed a reconnaissance geologic map of the Rattlesnake Hills 1:100,000-scale Quadrangle in central Wyoming. Located north of Jeffrey City and west of Casper, the area encompasses part of the Granite Mountains. The project was funded in part through grants from the U.S. Geological Survey’s STATEMAP program.
Project geologists Wayne M. Sutherland and W. Dan Hausel prepared the map by compiling available geologic maps along with reconnaissance field mapping and aerial photo interpretation. The map area lies within the central part of the Wyoming craton and includes the Gas Hills uranium district, the Rattlesnake Hills gold district, and the Tin Cup ruby and jade district.
Rising gold prices make the northeastern part of the quadrangle especially interesting since it encloses the Rattlesnake Hills gold district. Significant gold anomalies were discovered in this district in 1981 by W. Dan Hausel, which led to considerable gold exploration over the next two decades. Hausel mapped the area in detail in 1994 and 1995. Exploration in the district by some major gold companies led to several additional discoveries, including a large-tonnage, low-grade deposit that has potential to host more than one million ounces of gold.
The Tin Cup district in the southwestern part of the quadrangle includes several jade occurrences, as well as the Red Dwarf corundum (ruby and sapphire) deposit. Mapping by Hausel in 1996 showed that this corundum occurrence is localized in a nearly mile-long outcrop of gneiss. Samples of corundum recovered from the deposit have been as large as 2.5 inches across.
Sutherland and Hausel identified some interesting mineral occurrences during the mapping project, including some sapphires, jade, tourmaline, and copper. Entitled Preliminary geologic map of the Rattlesnake Hills 1:100,000-scale Quadrangle, Fremont and Natrona counties, central Wyoming, Open File Report OFR 02-2 is available over-the-counter at the WSGS office in Laramie or by mail. The black and white map (folded only) and accompanying report sell for $6.50 plus 6% sales tax when purchased over the counter. For mail orders include $2.55 postage and handling; Wyoming addresses should also include 6% sales tax.
from the Office of the Wyoming State Geologist
Ron Surdam, State Geologist