Monday, November 23, 2009

Geologic structure of Kartchner Caverns

Arizona State Parks Science & Research Manager Bob Casavant offered a new structural model for the origin of the faults that control the origin of Kartchner Caverns in southern Arizona, that is going to be controversial. Bob proposes a Laramide episode of transpressional faulting, with the block of Paleozoic sediments hosting Kartchner caught between fault strands. Basin and Range normal faulting followed, dropping the block down the east side of the Whetstone Mountains. [right, Big Room. Credit, Kartchner Caverns State Park]

Bob presented his model at an informal workshop at the caverns Discovery Center this morning to a group of hydrologists, geologists, and others who are engaged in the EIS process for the Rosemont copper mine. The idea was to look at some of the complexities of mountain fronts, carbonate reservoirs, and groundwater flow. Also presenting was Geary Schindel, Chief Tech Officer for the Edwards Aquifer Authority in San Antonio, Texas, who described karst aquifer behavior and management.

Part of the discussion centered on the potential for encountering karst terrain in the Rosemont mine excavations. Mine geologist Jeff Cornoyer reported that they had not encountered any caves in the more than 320,000 feet of holes drilled in the mine area.

One of the more surprising slides Bob Casavant showed was of an EM survey by hydroGEOPHYSICS, across the Kartchner Caverns fault block. The known cavern rooms stood out clearly. But there were also other, similar anomalies that may show undiscovered rooms to the west of the current cave complex, deeper under the mountains. Bob nicknamed the largest anomaly, the "West Wing."

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