A review of ags digest 22: ores and orogenesis :
Circum-Pacific Tectonics, Geologic Evolution, and Ore Deposits, eds., J.E. Spencer and S.R. Titley, 2008.

Peter D. Tillman (Consulting Geologist, Arizona and New Mexico, USA)

Digest 22 is the proceedings of the Arizona Geological Society's 2007 symposium. Since I wasn't able to attend the meeting, I was pleased to be asked to review the Digest.

Generalized geologic map of Sikhote-Alin, Russian Far East. (Ernst et al., Orogeny and Metallogenesis along the Margin of Eastern Asia)

It's interesting to see how the Digests have evolved over the 30-some years that I've been reading them. They have always been quality productions, well-bound and sturdy. The most striking difference is the generous use of color in recent volumes. Digest 22 is a solidly-hardbound oversize volume, handsomely produced, and a credit to the work of Editors Jon Spencer and Spencer Titley, and production manager Claudia Stone. It would be a worthy addition to your professional library.

At 600+ pages and 40+ papers, I can only mention a few papers here that I found particularly useful and interesting.

Karen Bolm and coauthors' "Using alluvial-basin ground-water chemistry to prospect for concealed porphyry copper deposits in Arizona," is a nice working memorial to her careful work -- her untimely death this past April was a shock to the local geological community. I've long been intrigued by the Copper Springs prospect southwest of Miami, AZ, an immature chalcocite-enrichment blanket that Bolm and coauthors sampled and discuss here. A fine example of how the use of color improves recent technical reports, and interesting reading for any copper explorationist.

Keith Long's "Economic life-cycle of porphyry copper mining" is a concise and penetrating review of this topic, and is particularly recommended for young geologists, or others new to porphyry copper geology and economics. His Figure 2, Grade-tonnage comparisons of porphyry copper deposits, deserved a half-page (or more) reproduction -- the quarter-page allotted is too small to make out all the details of this very busy chart, and it is one of the few presentation flaws I saw in the book.

Jon Spencer and Y. Ohara's "Magmatic and tectonic continuous casting in the circum-Pacific region" likens the formation of some lava extrusions and metamorphic core complexes to the industrial metal-casting process. It's a novel and plausible hypothesis, and the authors make their case with some impressive photography and digital graphics -- the color photos of the grooved hypabyssal diorite exposures at Sacsayhuaman, Peru are stunning. Perhaps even more impressive is that this paper was presented in place of a no-show at the conference -- a remarkable ad-lib!

Terry Hoschke's "Geophysical signatures of copper-gold porphyry and epithermal gold deposits" presents data on six western Pacific and one Andean deposits, including Batu Hijau and Grasberg (Indonesia) and Alumbrera, Argentina. This is required reading for explorationists who use geophysical data. Dr. Hoschke's presentation is aided by the generous use of fine, well-reproduced color graphics.

Ray Ingersoll's "Reconstructing southern California" is a clear and nicely-done review of current work there. As the author notes, "Reconstructing this complex history is an extraordinarily challenging and rewarding endeavor."

There are another 37 papers to go: See the table of contents which can be previewed on our website frontpage.

Digest 22 and the Symposium were both dedicated to Bill Dickinson, who has made many contributions to the subject areas, and continues to do so in his very active retirement. So raise a glass to Bill, one of the shining stars in our profession!

Happy reading!
Peter D. Tillman

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