Geologic descriptionThis prospect consists of altered bostonite dikes that cut feldspar porphyry; the dikes contain allanite, probably betafite (a uraniferous niobate mineral), and abundant magnetite. Samples of the bostonite contain up to 400 ppm uranium and 550 ppm thorium (Miller and Elliot, 1977). Barker (1991) investigated this area to evaluate reports that the intrusive rocks contain as much as 1.51% rare earth elements (REE). He describes the rocks as an intrusive complex of small stocks and dikes of syenite and monzonite that cover an area about 2000 feet in diameter. These plutons intrude Cretaceous andesite. The monzonite stocks form the center of the complex and vary from aphanitic feldspar porphyry to amphibole-rich hornblende porphyry. Syenitic and/or trachytic intrusive rocks occur as xenoliths and as dikes cross-cutting the monzonitic rocks. Tourmaline and magnetite occur on fractures in the monzonite and syenite. The syenite also contains minor purple fluorite. Chip samples of the most radioactive rocks contain a similar content of uranium and thorium as those reported by Miller and Elliot (1977). However, these samples failed to confirm the reported high values of REE, they contain near-normal background levels of lanthanum, cerium, and yttrium. |
| Geologic map unit |
(-155.805754895869, 66.2286392348195) |
| Mineral deposit model |
Felsic plutonic U-REE (Nokleberg and others, 1987) |
| Age of mineralization |
The intrusive complex probably is an apophysis of the Zane Hills pluton which is Cretaceous based on a K-Ar date of 81 Ma. |
| Alteration of deposit |
The bostonite dikes are described as altered, but details of the alteration are not given. |
