The mineralization at the Atlanta site occurs at the contact between younger Tertiary rocks and older Paleozoic sedimentary rocks. The Tertiary volcanic rocks are primarily felsic tuffs erupted during a period of intense ash eruptions that occurred across east-central Nevada approximately 28 million years ago. Included with the tuffs are local sediments and landslide debris derived from the ash deposits. The Paleozoic rocks are limestone, dolomite and quartzite that were deposited in a shallow marine environment approximately 400 million years ago.
These two different assemblages of rocks were juxtaposed against each other by movement along the Atlanta Fault. The Atlanta Fault is a normal fault where rocks in the hanging wall have slid down relative to the rocks in the footwall. In this instance, the volcanic rocks on the west of the north-trending Atlanta Fault have moved down relative to the Paleozoic sediments to the east.
Repeated movement of the fault fractured and dislocated the rocks on either side, creating a broad zone of fault breccia. The subsequent introduction of hydrothermal fluids replaced and cemented the breccia fragments with silica and introduced gold and silver.
These gold bearing jasperoids were the ore-host for past mining and are the primary target for current exploration.
Relogging of past RC holes resulted in the interpretation that drill cuttings, previously interpreted as part of the Tertiary volcanic rocks, were in fact a quartz latite intrusive porphyry that underlies the volcanic section. Recent U-Pb age dating has established that the porphyry is 35.9 +/- 0.4 Ma.
The 2011 drilling has confirmed that the porphyry contains gold.
At present, the geometry of the porphyry has not been determined and it remains open to the west, north and south. Though the gold mineralization in the porphyry and the Atlanta Fault are likely related, the porphyry is an “excellent exploration” target in its own right.