Rosemont geology report enters controversy

Two weeks ago the AZGS released a new geologic map and report (1) on the Rosemont area of the Santa Rita Mountains, where a copper mine is proposed.

The mine is stirring up opposition to its potential environmental and visual impacts. This has led to erroneous claims that our report states the mine site is geologically unstable. Unfortunately, the Pima County supervisors included this mistaken claim in their resolution unanimously opposing the mine.

As a result, the mischaracterization of our geologic report was getting wider circulation including being used to justify a call to change designation of the federal lands involved. Before this went further, I felt we needed to clarify just what our report did and did not say. I sent letters to Richard Elias, chair of the Pima County Board of Supervisors and Supervisor Ray Carroll, pointing out the problems. We have posted these letters on the AZGS website (www.azgs.az.gov – the link is bottom center).

In my letter to Supervisor Elias, I wrote,

“Our report is a geologic study of the rocks at the Earth’s surface in the Rosemont area. It makes no comments about any possible or proposed mine or mine pit design, nor does it specifically address any mining engineering issues. It certainly does not address the stability of any rock units in the map area under present conditions or under possible mining conditions. Mine design and pit wall stability are issues dealt with by mining engineers, and were not addressed in our geological report.

The faults mapped and described in the report are remnants of the forces that created the mountains millions of years ago and we found no evidence that they are active. The geometry of the faults and rock units in the map area is described by our report which can be used by mining engineers as one of many resources in designing a mine.”

It is in no ones interest to have misinformation circulating about such an important issue. On one hand, it raises unfounded concerns about the mine, and on the other, it brings into question the credibility of the mine opponents arguments.

There is a serious debate going on about mining in the region and the resulting impacts, both good and bad. I hope our clarification of the geologic report can help focus the discussion on the real issues at hand.

(1) “Geologic Map of the Rosemont area, northern Santa Rita Mountains, Pima County, Arizona,” by Bradford Johnson and Charles Ferguson, AZGS Digital Geologic Map 59.