Boston Ridge

Location: Alaska, United States (66.229, -155.803 approx.)

Commodities: rare earth elements; thorium; uranium

Deposit model: felsic plutonic U-REE · unclassified

Geology

The Boston Ridge prospect consists of a multi-phased intrusive complex occupying an area about 2000 ft in diameter on Boston Ridge. At the center of the complex several small monzonite stocks are composed of gray to green, fine-grained, amphibole-rich hornblende porphyry. This textural phase appears to grade to, or is cored by a gray aphanitic feldspar porphyry of similar composition which forms the core of two distinct topographic knobs on the portion of Boston Ridge shown in figure 6. Major oxide analyses of sample 31 and 35 suggest the composition to be of an undersaturated intermediate sub-volcanic rock termed tristanite. Within the porphyry phases, inclusion of syenitic xenoliths and cross-cutting syenite or trachyte dikes indicate at least two widely spaced events of either syenite or monzonite intrusion. Either two phases of syenite intrusion took place, one predating and the other post dating the monzonite, or two phases of monzonite, predate and postdate the syenite. Additionally, other dike phases include a leucocratic amphibole dacite and a biotite monzonite, both of which cut the stocks and andesite country rock. Only minor mineralization was observed at the prospect. Trace amounts of fluorite occur in syenite." (Barker (1991c))

Record imported from USGS USMIN ver. 4.0 (June 2019). Developments after that date appear on facility records, not here; see the methodology.