2009 Portland GSA Annual Meeting (18-21 October 2009)

Paper No. 9
Presentation Time: 10:30 AM


NOURSE, Jonathan A., Geological Sciences Department, Cal Poly Pomona University, Pomona, CA 91768 and IRWIN, James J., Colibri Resource Corporation, 803-1720 Balsam Street, Vancouver, BC V6K3M2, Canada, janourse@csupomona.edu

We report new geological mapping and assays from the Leon Property, located southwest of El Creston molybdenum deposit, 6600 hectares of claims that cover several old mine districts currently under option to Colibri Resource Corporation (TSX-CBI). Spatial distribution of rocks, structures and metals suggests that the Leon Property represents at least part of the El Creston porphyry system, exhumed in the lower plate of a northeast-dipping, mid Tertiary detachment fault system. The El Creston ore body (mapped and drilled by AMAX Exploration in 1981) is hypothesized to have been displaced northeastward 3 to 5 km from ground exposed on the Leon Property. Widespread molybdenum-copper-zinc mineralization occurs in footwall rocks and soils of the Leon Property directly adjacent to mapped detachment fault(s), including the old La Fortuna underground copper-moly mine workings. Several kilometers WSW are vein systems with gold-silver-lead-zinc mineralization, believed to be distal mineralization associated with the same porphyry system.

Mineralization on the Leon Property probably occurred in two pulses spatially associated with quartz veins in hydrothermally altered country rock. Host rocks commonly altered to hematite, limonite, sericite and kaolinite include Proterozoic gneiss and granite, Late Cretaceous granodiorite, Late Cretaceous(?) diorite, early(?) Tertiary rhyodacite porphyry, and mid(?) Tertiary leucocratic biotite monzogranite. Two sub-parallel detachment faults separate these mineralized footwall rocks from a hanging wall composed of Paleoproterozoic granite overlain by Neoproterozoic(?) quartz sandstone. These faults may represent up-dip extensions of the El Creston and Gemini faults (Leon and Miller, 1981), down dropped to the southwest along a N30W striking normal fault.

Colibri Corporation has collected and assayed hundreds of rock chip and soil samples. These samples delineate strong molybdenum, copper and zinc mineralization within the footwall block adjacent to the detachment fault. Soil assays exceed 200 ppm molybdenum and 1000 ppm copper over an area greater than 2 km2; chip samples from quartz veins and altered granodiorite host rock average 580 ppm molybdenum. Diamond core drilling demonstrates comparable assays, including a 72 m intercept averaging 0.195% (1950 ppm) Mo.