A geologic map and a bulletin describing the geology and mineral deposits of Gillespie County, Texas, are being prepared by the Bureau of Economic Geology. Awaiting completion of this map and bulletin, abbreviated mimeographed circulars describing the more important mineral deposits are being issued by the Bureau. The first scheelite recognized in Gillespie County was mentioned in a recent circular. Work Project No. 18926 was first engaged in an examination of soapstone deposits in the county and later spent some weeks in an examination of the scheelite at the old barite prospect and vicinity. At the termination of the WPA project, the investigation was continued by the Bureau of Economic Geology and was extended to include the rest of the pre-Cambrian area of Gillespie County. In the preparation of this report, acknowledgment is made to Dr. V.E. Barnes under whose supervision the work was done.

Scheelite occurs in the pre-Cambrian rocks of northern Gillespie County as a vein and contact metamorphic mineral. This mineral, when viewed under an ultraviolet light source of the right wavelength, fluoresces a bluish white when pure and white to yellow when it has a progressively higher molybdenum content. The discovery of scheelite in this area is directly attributable to the use of an ultraviolet mineral lamp. Since scheelite is heavy, a method of prospecting similar to that used in tracing gold to its source was tried. The streams of the area were panned, and in those containing scheelite, an effort was made to trace it to its source. In addition, scouting for areas of contact metamorphic minerals was done by day, and favorable areas were examined with the mineral lamp at night.