Constraining the tectonic setting of mineral deposits using geochemical fingerprinting
Many large lead-zinc deposits are accompanied by major barite mineralization. While the barite itself is not particularly valuable, it provides a useful indicator of deeper Pb-Zn. However, there are many barite deposits that do not have associated Pb-Zn. Those with Pb-Zn are found in rifts whereas those without are found in accretionary prisms of subduction zones (Maynard and Okita, 1991).
The issue is to find a predictive tool that would quickly flag a barite deposit from an unknown tectonic setting as prospective or barren. We have had some success with using Sr isotopes (Maynard et al., 1995). Deposits with Sr more radiogenic than seawater are typically associated with rifts and therefore are more prospective for Pb and Zn. Those with seawater values or lower do not have Pb-Zn.
Geochemistry of interbedded volcanics
Note in the figure above some overlap of Sr values for the Nevada deposits. Also notice the appearance of a third tectonic category: strike-slip. This category was recently identified and characterized from the California Borderland by Hein et al. (2007). We see a better separation of these three categories using ratios of trace and minor elements
Applying this diagram to the Nevada deposits, we see that they fit best in the strike-slip category, as also concluded by Koski and Hein (2003).
Hein, J.R., Zierenberg, R.A., Maynard, J.B., and Hannington, M.D., 2007, Barite-forming environments along a rifted continental margin, Southern California Borderland: Deep-Sea Research Part II., v. 54, p. 1327-1349.
Koski, R.A., and Hein, J.R., 2003. Stratiform barite deposits in the Roberts Mountains Allochthon, Nevada: A review of potential analogs in modern sea-floor environments. In: Bliss, J.D., Moyle, P.R., and Long, K.R., eds., Contributions to industrial minerals research. U.S. Geological Survey Bulletin 2209-H, 17 p; (http://pubs.usgs.gov/bul/b2209-h/).
Maynard, J.B., and Okita, P.M., 1991, Bedded barite deposits of the U.S., Canada Germany, and China: Two major types based on tectonic setting: Economic Geology, v. 86, p. 364-376.
Maynard, J.B., Morton, J., Valdes-Nodarse, E.L., and Diaz-Carmona, A., 1995, Sr isotopes of bedded barites: a guide to tectonic setting with implications for Pb-Zn mineralization: Economic Geology v. 90, p. 2058-2064.