Inmachuk

Prospect, Active

Alternative names

Hannum

Commodities and mineralogy

Main commodities Pb; Zn
Other commodities As; Ba
Ore minerals arsenopyrite; galena; pyrite; sphalerite
Gangue minerals barite; calcite; limonite; quartz

Geographic location

Quadrangle map, 1:250,000-scale BN
Quadrangle map, 1:63,360-scale D-3
Latitude 65.9212
Longitude -163.3216
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Inmachuk prospect is on the west bank of Hannum Creek, about 1,000 feet upstream from the mouth of Cunningham Creek. Hannum Creek is a north tributary to Inmachuk River. The prospect is about 0.3 west of the center of section 16, T. 6 N., R. 22 W. The location is accurate.

Geologic setting

Geologic description

The rocks in the area consist of a Paleozoic, poorly exposed, interlayered sequence of pelitic schist and schistose dolomitic marble that strikes northwest and dips 15 to 65 degrees north (Till and others, 1986; Hawley, 2007; Stevens, 2008) . Part of this metasedimentary sequence is siliceous and described as quartzite (Herreid, 1966). Herreid considers the quartzite here and at Harrys Creek (BN055), 4,000 feet to the northwest, to be silicified marble. Hudson and others (1977) described outcrops of the silica-rich rock on Harrys Creek as siliceous schist. The frozen ground in the Hannum prospect area has handicapped efforts to expose bedrock (Mulligan, 1965; Herreid, 1966). Most of the area is covered by surficial material that obscures the structure of the rocks.
The prospect has been known since 1906 and there has been considerable activity since 1966 when Bunker Hill Mining Company dug about 1,500 feet of trenching in at least 6 trenches, drilled 15 core holes, and collected numerous soil samples that defined several zones of anomalous zinc and lead (Hawley, 2007; Stevens, 2008). The mineralization is only locally exposed in the trenches; a 30-foot-wide gossan zone within marble is exposed in one trench. Mineralization is apparently pods and stringers of sulfides, primarily galena, sphalerite, and pyrite, in silica-rich rock. An assay of a 6-foot -wide siliceous zone contained 0.05 percent copper, 0.38 percent zinc, 0.12 percent lead, and no silver and gold (Herreid, 1966). Soil samples collected upslope 125 to 375 feet to the west, contained lead and zinc values up to more than 1,000 parts per million. Soil samples near the prospect commonly contain more zinc than lead (Herreid, 1966). From 2002 to 2005, Royal Pretoria Mines in their own behalf and in 2006 for Full Metal Minerals did considerable work in the area and defined a large anomaly that covered the prospect and the Harrys Creek prospect (BN055) (Hawley, 2007; Stevens, 2008). Although it is likely that the mineralization at the Hannum prospect continues west to the Harrys Creek prospect (BN055), this has not been confirmed.
In September, 2007, Millrock Resources Inc. (Stevens, 2008) drilled 5 holes that totaled 644.1 meters to test the Inmachuk mineralization. The drilling was spread along a line about 1,300 meters long on the south side of Cunningham Creek, northwest of the mouth of Hannum Creek. The drilling was along a zone that is strongly anomalous in zinc (Hawley, 2007). Mineralization was intersected in three of the holes and consists of oxidized lead-zinc minerals. The best intercepts were: 3.05 meters with 12.34 percent zinc; 6.61 meters with 2.06 percent zinc; 0.61 meter with 5.55 percent zinc and 3.66 percent lead; and 0.91 meter with 4.56 percent zinc. The mineralization apparently occurs in flat-lying pods that replace marble. The pods are generally narrow and low grade and the mineralization seems to thin down-dip. MIllrock relinquished the property to Full Metal Minerals in March, 2008.
Geologic map unit (-163.324305431282, 65.9205031247454)
Mineral deposit model Sphalerite-galena replacement pods in marble.
Age of mineralization The deposit may be epigenetic and younger than the host schist and marble; epigenetic deposits on the Seward Peninsula are primarily Cretaceous. If it is stratiform and syngenetic, it is Paleozoic.
Alteration of deposit Pervasive development of silica-rich rock in the marble. The deposit is deeply weathered and oxidized.

Production and reserves

Workings or exploration At least six trenches were dug with a bulldozer in the mid-60s along the west bank of Hannum Creek. The trenches total about 1,500 feet but they only locally expose mineralization. Fifteen core holes were drilled in 1966. Five holes totaling 644.1 meters were drilled in 2007; three intersected mineralization.
Indication of production None
Reserve estimates None.
Production notes None.

References

MRDS Number A012715

References

Hawley, C.C., 2007, Inmachuk exploration project, Seward Peninsula, northwestern, Alaska: NI 43-101 Technical Report for First Factor Developments, Inc., 57 p. (Posted on www.sedar.com, June 25, 2007, under Millrock Resources, Inc.)
Millrock Resources Inc., 2008, Millrock announces results of drilling at Inmachuk project, Seward Peninsula, Alaska: http://millrockresources.com/index.php/news/millrock_announces_results_of_drilling_at_inmachuk_project_seward_peninsula (News release, March 28, 2008).
Stevens, D.L., 2008, Inmachuk prospect, Fairhaven mining district, Seward Peninsula, Alaska: NI 43-101 Technical Report for Millrock Resources, Inc., 41 p. (Posted on www.sedar.com, June 6, 2008).
Reporters Travis L. Hudson (Applied Geology); D.J. Grybeck (Contractor, U.S. Geological Survey)
Last report date 4/2/2010