A report about the economic geology of four mines located in the Helvetia mining district in the Santa Rita Mountains in south central Arizona. The sedimentary rocks in Helvetia range from Cambrain to Cretaceous.

From introduction: The exploration project at Christmas was carried on cooperatively by the Geological Survey and U. S. Bureau of Mines. Mr. 0. M. Bishop, Engineer for the Bureau of Mines, examined the property and in his report of June 6, 1942 recommended that six holes be drilled from the 800 level of the mine. The Bureau of Mines began drilling in September 1942, and the Survey investigations began a month later. Since any ore bodies discovered below the 800 level would be inaccessible until a deeper level could be developed, the Bureau and Survey decided to explore from higher levels where resulting benefits could be more quickly realized. Drilling from the upper levels was begun early in 1943.

From abstract: At the request of the Council of the San Carlos Apache Tribe the U. S. Geological Survey entered into a cooperative agreement calling for a brief reconnaissance study to determine, as far as practical, the mineral potential of the San Carlos Indian Reservation. Five months of field work was done during the winter and spring of 1952-53. About 30 percent of the reservation is covered by alluvial deposits of late Tertiary, Pleistocene, and Recent age, and another 60 percent is covered by volcanic rocks of Tertiary and perhaps Pleistocene age. These rocks are younger than the major epochs of metallization in southeastern Arizona. The remainder of the area is underlain by pre-Cambrian and Paleozoic sedimentary rocks, pre-Cambrian granite, and pre-Devonian diabase.