Abstract by Alec Martin
Swiss Army Titanite – A versatile indicator mineral in a Mo-W Porphyry Deposit
Hosted within the Oligocene Little Cottonwood Stock (LCS) of central Utah are two younger granitic phases, the White Pine (WP) and Red Pine (RP) porphyries. Geochemical evidence suggests that the WP was generated from a separate magma than the main LCS, and then differentiated to form the RP. Mo-W mineralization and associated alteration are centered on the RP porphyry. Titanite, with its variable geochemical signatures, can be used to fingerprint each of these different lithologies and test their genetic connections. Magmatic RP titanite has higher Fe-Al ratios and relatively distinct Ca, Ti, F, and REE contents compared to the WP and LCS titanite; similar differences exist for WP when compared to LCS titanite. Although hydrothermal titanite varies in composition across all three lithologies, the breakdown of magmatic WP and RP titanite to quartz, apatite, ilmenite, rutile, allanite, and monazite, and the absence of magnetite or hematite as in the LCS, are evidence for a low fO2 of the system at the time of alteration, attested to by the presence of ore minerals such as scheelite and lack of powellite or wolframite.