The significance of a widespread stream sediment copper anomaly in the Batamote Mountains, Pima County, Arizona

Abstract

To determine the cause and distribution of a widespread copper anomaly in the Batamote Mountains discovered by the U. S. G. S. (Barton and others, 1982), detailed stream sediment and heavy mineral concentrate sampling and reconnaissance geologic mapping were undertaken in the area. The stream sediments yielded two anomalous areas characterized by copper, silver and bismuth, separated by a narrow trough of low values. The anomalous values are spatially associated with a series of northerly trending normal faults. The anomalous copper is held predominantly in iron and manganese oxides, but a significant portion is held in a reduced form (probably organics). Analysis of pyrite grains from heavy mineral concentrates for copper indicates that pyrite cannot contribute enough copper to cause the observed anomalies. Analysis of the non-magnetic fraction of heavy mineral concentrates produced a similar anomaly pattern for copper, but no enhancement was realized relative to stream sediments. This analysis also yielded three other anomalous areas characterized by a volatile element assemblage, a tin-molybdenum assemblage and a silver-arsenic-molybdenum assemblage, respectively. The cause of these anomalies remains problematic. The primary anomaly is best explained as the result of dispersion along normal faults. The original source of the metals in the normal faults could not be absolutely determined in the present study.