Age constraints on host rocks of Los Uvares gold deposit: Magmatic pulses in southernmost Baja California, Mexico
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Abstract
Los Uvares disseminated gold epithermal deposit, in the central part of the Cabo San Lucas Block (CSLB) near the tip of Baja California peninsula, occurs in a cataclastically deformed tonalite intruded by alaskite and mildly faulted diorite dikes. Potassium-argon (K-Ar) isotopic ages on hornblende separates from relatively unaltered intrusive rocks at Los Uvares are: 137 ± 6 Ma (tonalite) and 128 ± 5 Ma (diorite). The K-Ar ages are internally consistent with the relative ages of diorite and tonalite from field relationships, suggesting a Cretaceous magmatic event. These ages are older than previous ages found for similar plutonic rocks in the CSLB (ranges of 109-42 Ma). It seems likely that the Los Uvares deposit occurs in an intrusive complex that repre- sents an older phase (not previously reported) of the Cretaceous-Tertiary magmatic pulse in the CSLB. Fission-track ages on apatites in the diorite dikes range from 80 to 100 Ma. Fission-track data suggest that hydrothermal activity at Los Uvares ended by ~80 Ma, and that cooling/erosion followed.
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