Copperstone occurs within the "Basin and Range" province of the south-western USA. The regional geology is strongly influenced by Tertiary age detachment faults and younger high angle normal faults. The Copperstone gold deposit is related to the Moon Mountain or Copper Peak detachment fault. Gold mineralization at Copperstone occurs principally within the moderate to low-angle Copperstone Fault which has been interpreted to be a listric fault associated with the underlying Moon Mountain detachment fault. Gold occurs as native flakes within fault breccia, gouge and shear zones related to the faulting. The wall and host rocks are typically Triassic sediments and Jurassic quartz latite volcanics. Gold is commonly associated with hematite, chlorite, quartz, manganese oxide and copper oxide mineralization.
In the case of the Copperstone Mine, the gold is not encapsulated in sulphides or silica, and the ores do not contain active carbon. This means that the ores at Copperstone are not refractory. This is a consequence of the fact that these ores appear to be comprised of "original", or "primary", or "hypogene" oxides minerals. So Copperstone is not a weathered or oxidized material that started off as a sulphide (which is the common case). The oxides, when ground in the mill, free the gold up to be recovered in the gravity or flotation circuits. These ores also respond very well to cyanide processes.
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