Tapisaghak River Occurrence, Bering Sea Mining District, Nome Census Area, Alaska, USAi

Regional Level Types
Tapisaghak River Occurrence	Occurrence
Bering Sea Mining District	Mining District
Nome Census Area	Census Area
Alaska	State
USA	Country

Location: Tapisaghak River is a north-flowing stream that drains the Kinipaghulghat Mountains at the east end of St. Lawrence Island. This site includes all the southwest tributaries of the river. This area was not included by Cobb (1972; 1980).
Geology: The Tapisaghat River has headwaters that drain the main part of the mid-Cretaceous (104 +/1 3.1 Ma) Kinipaghulghat pluton (Csejtey, Patton, and Miller, 1971; Patton and Csejtey, 1980). This 65 square mile pluton makes up the resistant upland on the east end of St. Lawrence Island. It is a composite intrusion that contains several phases including monzonite, syenite, biotite quartz monzonite, quartz monzonite (granite), and alaskite (Csejtey, Patton, and Miller, 1971, Figure 6). Monzonite and syenite appear to make up discontinuous border phases on the north and south sides of the main pluton. Biotite quartz monzonite makes up the main part of the pluton and has border phases developed against monzonite and syenite. Quartz monzonite (granite) and alaskite forms small intrusive bodies that are emplaced in monzonite, syenite, and biotite quartz monzonite. Two hypabyssal latite to quartz latite intrusions are intruded in the northeast part of the pluton. Stream sediment samples, particularly from the western headwater tributaries of the Tapisaghat River, contain 10 to 15 ppm tin, up to 5 ppm beryllium, and one contains 200 ppm boron (Patton and Csejtey, 1972). Bedrock in the area of these anomalies includes small (about 1/2 mile across) alaskite intrusions into monzonite, syenite, and biotite quartz monzonite (Csejtey, Patton, and Miller, 1971, Figure 6). Specific data for bedrock in these drainages are not available but quartz monzonite (granite) and alaskite from this pluton are reported to be intensely altered to sericite, chlorite, and some epidote (Csejtey, Patton, and Miller 1971, p. D73). Float of tourmaline-rich granite samples from unidentified streambeds of eastern St. Lawrence Island have high (but unspecified) tin values (Patton and Csejtey, 1971, p. 7).
Workings: Stream sediment samples, particularly from the western headwater tributaries of the Tapisaghat River, contain 10 to 15 ppm tin, up to 5 ppm beryllium, and one contains 200 ppm boron (Patton and Csejtey, 1972).
Age: Potential tin mineralization in this area would be similar in age to that of the host intrusive rocks. The one K/Ar age from the Kinipaghulghat pluton is for biotite from the monzonite and syenite on the south side of the pluton. This age, 104 +/- 3.1 Ma (Patton and Cesjtey, 1980), may not accurately reflect the age of the more felsic and late-forming intrusions potentially associated with tin mineralization elsewhere in the pluton. However, a mid- to Late Cretaceous age for the potential tin mineralization is indicated.
Alteration: Specific data for bedrock in these drainages are not available but quartz monzonite (granite) and alaskite from this pluton are reported to be intensely altered to sericite, chlorite, and some epidote (Csejtey, Patton, and Miller 1971, p. D73). Float of tourmaline-rich granite samples from unidentified streambeds of eastern St. Lawrence Island have high (but unspecified) tin values (Patton and Csejtey, 1971, p. 7).

Commodities (Major) - Sn
Development Status: None
Deposit Model: Cassiterite-bearing vein or greisen in felsic intrusive rocks. Deposit models 15

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Link to USGS - Alaska:	SL023

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