TITANITE IN PEBBLE DIKES IN THE EAST TRAVERSE MOUNTAINS, CENTRAL UTAH, AND ITS IMPLICATIONS FOR THE FORMATION OF MO-W DEPOSITS

Titanite (Ttn) from pebble dikes in the East Traverse Mountains of central Utah can elucidate the crystallization history of the White Pine (WP) and Red Pine (RP) porphyries ~16 km east in Little Cottonwood Canyon. The explosive emplacement of the pebble dikes involved hydrothermal fluids (either magmatic or meteoric or both) near the still hot Little Cottonwood intrusive complex. The pebble dikes were injected into the upper parts of the WP, RP, Little Cottonwood Stock (LCS), and the overlying strata which are represented by clasts in the dikes. The East Traverse Mountain mega-landslide then transported several of the pebble dikes away from the intrusive center, which subsequently underwent tectonic uplift, erosional denudation, and substantial glaciation.

Electron microprobe and laser ablation analyses of Ttn in granitic clasts preserved in pebble dikes provide geochemical data for parts of the intrusive centers that have since been eroded away, perhaps completely. Of particular note is the presence of highly porphyritic and relatively unaltered RP clasts preserved in the pebble dikes, in situ samples of this phase are rare and heavily altered. Ttn from these porphyritic RP clasts have distinctive compositions compared to Ttn in other intrusive units in the area, such as lower Ti, Ca, Nb, Mo, and W, and higher Sn and Mn. These Ttn compositions provide a glimpse into sections of the apical zone of the now eroded WP-RP porphyry system, which sheds new light on the nature of hydrothermal alteration and mineralization in the area. In opposition to some Mo-W systems, where titanite Mo values are elevated (120ppm+) in the mineralizing granite, Mo values in titanite in the LCS-WP-RP system decline (averaging 45 to 29 to 18, respectively) approaching the mineralizing RP intrusion, giving an example of the potential misuse for titanite as an indicator mineral for Mo-W mineralization.