Cretaceous-early Tertiary history of the northern Pyramid Mountains, southwestern New Mexico
Charles H. Thorman and Harald Drewes
The Pyramid Mountains are a north-trending range of Lower Cretaceous through middle Tertiary volcanic and plutonic rocks in the Basin and Range province of southwestern New Mexico southwest of Lordsburg. The Lordsburg and Pyramid mining districts produced about $59,270,000 worth of copper, silver, lead and gold between 1870 and 1973 (Thorman and Drewes, 1978). A detailed geologic study of the Lordsburg district was made by Lasky (1938), and general study of the Lordsburg 15-minute quadrangle was made by Flege (1959). Clark (1970) described mineral zonation in the district.
The Cretaceous-early Tertiary history of the northern Pyramid Mountains, presented here, is based on new detailed map-ping of the Gary and Lordsburg 7.5-minute quadrangles (fig. 1) by Thorman and Drewes (1978). Refinements and revisions to the previous geology are shown in Figure 1. Foremost among these revisions was the recognition of Lower(?) Cretaceous sandstone. The Upper Cretaceous basalt of Lasky (1938) is seen to consist of two units of Late Cretaceous and one of Paleocene age, all of andesite. The granodiorite stock is older, not younger as concluded by Lasky, than a unit of rhyolite intrusives. Mineralization of the district probably occurred about 55 to 57 m.y. ago.
The Pyramid Mountains lie within the area of Paleozoic carbonate-shelf deposition typical of southwestern New Mexico and southeastern Arizona, and about 40 km southwest of the west-northwest-trending Deming axis of post-Devonian age (Turner, 1962). Paleozoic rocks are not exposed in the Pyramid Mountains, although exotic blocks of Pennsylvanian lime-stone occur in Tertiary volcanic rocks of the central part of the range, and Pennsylvanian-Permian Horquilla Limestone underlies a low hill a few kilometers southwest of the range. Some aspects of the Paleozoic and Mesozoic history of the region are reviewed by Greenwood and others (1977).
- Thorman, Charles H.; Drewes, Harald, 1978, Cretaceous-early Tertiary history of the northern Pyramid Mountains, southwestern New Mexico, in: Land of Cochise, Callender, J. F.; Wilt, Jan C.; Clemons, R. E.; James, H. L., New Mexico Geological Society, Guidebook, 29th Field Conference, pp. 215-218.