Thunder Creek Occurrence, Yentna Mining District, Matanuska-Susitna Borough, Alaska, USAi

Regional Level Types
Thunder Creek Occurrence	Occurrence
Yentna Mining District	Mining District
Matanuska-Susitna Borough	Borough
Alaska	State
USA	Country

There are two Thunder Creeks in the database, each with an ADRF number. These two occurrences, about 0.6 miles apart, are two separate areas of placer workings and appropriately assigned their own ARDF numbers, despite the confusing use of the same name twice. Reed and others (1978) indicate that hydrothermally altered zones similar to those in Thunder Creek are observed along Dollar (TL031) and Thunder Creek (TL058), at the headwaters of Treasure (TL030), Dutch (TL033) and Bear Creeks (TL017) and at an unnamed locality east of McDoel Peak (TL053).
Location: U. S. Bureau of Mines (1998) shows this occurrence in the southeast quarter of Section 30, T. 28 N., R. 9 W., of the Seward Meridian. This locality is downstream about 0.6 miles from TL058. These two occurrences are two separate areas of placer workings, and appropriately assigned their own ARDF numbers, despite the confusing use of the same name twice.
Geology: This occurrence is located about 0.6 miles downstream on Thunder Creek from another occurrence also called Thunder Creek (TL058). No published description of this locality is available. The description for the other Thunder Creek location (TL058), given below, contains more details on the nature of the placer deposit, and because of its proximity, probably applies to this occurrence also. Clark and Hawley (1968) describe placer gold associated with an auriferous white quartz conglomerate and breccia deposits at Thunder Creek. The conglomerate is composed of angular quartz fragments mixed with a few rounded quartz and lithic pebbles in fine siliceous clay matrix. Thin layers of lignite are present within the conglomerate which indicate a Tertiary age (Clark and Hawley, 1968). The white quartz conglomerate placers (e.g. Willow Creek (TL042), Thunder Creek (TL032), and Dollar Creek (TL031)) represent the oldest placers in the Cache Creek area. Capps (1925) describes the white quartz conglomerate as the basal unit of the Tertiary Kenai Formation. However Clark and Hawley (1968) suggest that the white quartz conglomerate is older and that the Kenai Group was deposited on it. They believe the auriferous conglomerate is near its original source in part because the characteristics of the gold show a common source that has not moved far or has not been reworked. Further, they indicate that the conglomerate is a product of shearing and weathering in situ of argillic altered, auriferous Tertiary quartz porphyry intrusive rocks and associated quartz veins that were emplaced along northeast, high angle normal faults. The lineaments in Dutch and Cache Creeks represent two of these faults. From these paleo-channels gold was reconcentrated into Cache Creek in more recent time. (Mertie, 1919; Clark and Hawley, 1968; C.C. Hawley and Associates, Inc., 1978). Reed and others (1978) indicate that hydrothermally altered zones similar to those in Thunder Creek are observed along Dollar (TL031) and Thunder Creek (TL058), at the headwaters of Treasure (TL030), Dutch (TL033) and Bear Creeks (TL017) and at an unnamed locality east of McDoel Peak (TL053).
Workings: The drainage has been prospected and mined by various small scale surface methods.
Age: Tertiary and Pleistocene.

Commodities (Major) - Au, Sn, W; (Minor) - As
Development Status: Undetermined.
Deposit Model: Placer Au-PGE (Cox and Singer, 1986; model 39a).

Other Databases

Link to USGS - Alaska:	TL032

Other Regions, Features and Areas containing this locality

References