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BIOGENIC NITROGEN FROM TERMITE MOUNDS AND THE ORIGIN OF GERHARDTITE AT THE GREAT AUSTRALIA MINE, CLONCURRY, QUEENSLAND, AUSTRALIA

Erik B. Melchiorre^1,, Peter A. Williams², Timothy P. Rose³ and Becky C. Talyn⁴

¹ Department of Geology, California State University, 5500 University Parkway, San Bernardino, California 92407, U.S.A.
² Minerals and Materials Group, School of Science, Food and Horticulture, BCRI Parramatta Campus, University of Western Sydney, Locked Bag 1797, Penrith South DC, NSW 1797, Australia
³ Chemical Biology and Nuclear Science Division, Lawrence Livermore National Laboratory, Livermore, California 94550, U.S.A.
⁴ College of Natural Sciences, California State University, 5500 University Parkway, San Bernardino, California 92407, U.S.A.

E-mail address: emelch{at}csusb.edu

The Great Australia deposit, near Cloncurry, Queensland, Australia, hosts an unusual enrichment in the copper nitrate mineral gerhardtite. Nitrogen isotope analyses suggest that oxidized ammonia from nearby termite mounds provides the nitrate required for gerhardtite mineralization. Groundwater ¹⁵N and [NO₃ ^–] show a correlated decrease with depth, suggesting a surface source of nitrogen, with ¹⁵N_AIR > +10. The ¹⁵N values of gerhardtite (¹⁵N_AIR = +13.3) and local bulk termite-mound material (¹⁵N_AIR = +13.5) are virtually identical, and the remote desert location of the deposit precludes a septic or manure source of nitrogen. Similarly, remobilization of older inorganic evaporitic nitrates is an unlikely source owing to both geology and climate. Field evidence suggests that the spatial distribution of termite mounds may be a useful predictor of base-metal speciation as nitrates within the oxidation zone of base-metal deposits.

Keywords: gerhardtite, nitrogen, isotope, copper, Great Australia deposit, Australia.