VOLCANOGENIC LITHIUM AT THE ANDERSON URANIUM MINE, DATE CREEK BASIN, ARIZONA

Lithium at the Anderson uranium mine, northwest of Wickenburg, AZ is comparable to the lithium occurrence and structural setting of the Thacker Pass/McDermitt caldera complex, NV [Lithium Americas Corp.]. Uranium mineralization (average grade of 0.06 U₃O₈) at the Anderson mine has been known since 1955 and smectite from the Date Creek Basin sediments is enriched in lithium (0.21-0.39%). Both the Anderson uranium mine and the anomalous lithium are in Date Creek Basin sediments that are within the outline of the disrupted Miocene McLendon caldera. The Date Creek sediments are interpreted as intracaldera fill and are ~500 m thick. The McLendon caldera is defined by a funnel-shaped, -25 mgal gravity low and an extensive shoulder of 24.7 Ma intercalated andesites, rhyodacites, breccias, near-source debris flow, lithic-pumice tuff, and vitrophyre that is > 400 m thick. Approximately one-third to one-half of the ~20 km diameter caldera remains to the northeast and east of the mine and flow foliations dip to the northeast and east. Ash-flow tuff (23.9 Ma) is mapped at a nearby detachment fault. The volcanic section has average Th:U ratios of 4.5-2.4 which indicate minimal uranium depletion. Both the lithium and uranium occurrences are interpreted to be volcanogenic and related to late-stage caldera-forming processes and are not derived from the 24.7 Ma volcanic sequence. Anomalous arsenic, vanadium, and zirconium are also found in the intracaldera sediments. Economic lithium occurrences are mainly associated with salars/brines or pegmatites; however, lithium occurrences within structures such as the McDermitt or McLendon calderas indicate a sound volcanogenic exploration model.