SONORA PALEOCHANNEL
stockworks. In contrast, the Amadeus zone is a series of high-level epithermal Au-Ag veins (Bennett, 2010).
Paleozoic (Pzm) metamorphics in the vicinity of the quartz monzonite stock (Kqm, Figure 5), are Au-enriched in the west and Cu-Pb-Zn-Mo enriched in the east. Early phase chalcopyrite-sphalerite is overprint- ed by pyrite-pyrrhotite. Late-stage epith- ermal veins indicate multiple events. Some feldspar porphyry dikes postdate replace- ment and skarn mineralization, but do not host appreciable mineralization. Big Creek fault movement is younger than porphyry dike emplacement.
The strongly altered quartz monzonite
porphyry (Kqm) stock is also host to min- eralization. Au-Ag occur in multiple pyrite- chalcopyrite veins in the immediate wall rocks and in the matrix of the intrusive clast- supported breccia located along the intru- sive contact (Bennett, 2010). Tetradymite nuggets have been recovered from min- eralized quartz monzonite outcrops in the headwaters of Sonora Gulch, from outcrops of a vein near the mouth of Sonora Gulch,
and halfway between the boil box in George Wilson’s screen deck and wash plant.
Placer Mineralization
Placer mineralization at Hayes Creek is only known from hand sample observa- tion of nuggets from George Wilson, from personal descriptions by Jeff Bond, Yukon Geological Survey placer geologist, and inferred from comparisons with other, bet- ter described, Yukon placer deposits. Te mineralization appears to be restricted to tetradymite (Te2Bi2S) and Au mineraliza- tion to native Au. Au and Te do appear to cohabitate, however. Rounded, relatively soft nuggets of grey tetradymite tend to adhere to somewhat rounded, bright yel- low inclusions of Au in a manner similar to those examples from Miller Creek in the Sixty-Mile District (Photos #4 and #5). The tetrad- ymite appears, in these cases, to have catalyzed and pre- cipitated directly on the Au nugget surfaces.
When broken open, the higher grade
Photo #4. Annealed gold and tetradymite nuggets from Millers Creek, Sixty-Mile, Yukon.
tetradymite nuggets recovered by George Wilson have a grey metallic matrix. Nuggets of galena occur in the same gravity concen- trate as tetradymite, but when broken open are more crystalline, shiny and metallic. The smaller grains of tetradymite, galena, and other moderately heavy minerals are presumed lost over the riffles and discarded into tailings during normal placer opera- tions. The larger ones probably don’t make it past George Wilson’s 1.5” screen deck holes.
The panel of pay gravel being loaded into
George Wilson’s screen deck (Photo #6 is a detail of Photo #2) and was unfortunately not sampled during my 2010 visit. At the same time that the photo was taken, the black sands in the last few riffles coming off the screen deck (Photo #2) were sampled, however (Table 1, sample 100730.04), con- firming the presence, but not the grade, of Te in the pay gravel. The black sand in sample 100730.04 assayed 648 ppm Te, 29.5 ppm Au, and >1% Pb.
Photo #5. Annealed gold nuggets cemented with tetradymite, the tetradymite having grown onto miner’s blast cord left underground (and under water) for several decades prior to 1980’s at Millers Creek, Sixty-Mile District, Yukon.
www.aipg.org
Hardrock Te Geochemistry Geochemical highs of 35 ppm Te have
been reported in veined quartz monzonite porphyry at Sonora (Schultz, 2004, page 28). Assay results from mineralized Kqm rock chips in 1978 trench Te-1 included 4,290
ppm Te, 15,000 ppm Bi, and 41.0 opt Au. Assays of one interval from 1981 core hole 81-3 included 1,050 ppm Te, 4,000 ppm Bi, and 3.5 opt Au.
Placer Te Geochemistry High-graded placer nuggets assayed up
to 219,000 ppm Te and 258 gpt Au from the boil box of George Wilson’s screen deck in 2010. These samples were taken from concentrates derived from the upper gravel strata of the Sonora paleochannel (Photos #2 and #6). The highest-grade Te nugget
Photo #6. In-place panel of pay gravel of Sonora paleochannel being exca- vated by George Wilson on 30 July, 2010 (detail from Photo #2)
also assayed 4,112 ppm Ag, >10,000 ppm Bi, >10,000 ppm Pb, and 3,108 ppm W.
Black sand taken directly from the last
two riffles at the end of George Wilson’s sluice carried 648 ppm Te, 30 gpt Au, 2,237 ppm Bi, >10,000 ppm Pb, and 2,926 ppm W. Black sand tailings after Wilson pan- ning, black sand concentrate from a 2010 surficial bulk sample on lower Hayes Creek, and various gravels and old tailings sampled on 2010-0803 below the mouth of Sonora Gulch were also assayed (see Table 1 on page 16).
Discussion
Regional Geologic Discussion Geology and spatial relationships of the
Sonora Au-Cu porphyry system and the Hayes Creek placer district are typical of other Dawson Range porphyry deposits and prospects. Identifying and developing a Te deposit at Hayes Creek thus has eco- nomic implications for Te and Au potential elsewhere in the Dawson Range and the Alaskan to British Columbia Tintina Gold Belt. A good understanding of Quaternary stratigraphy and structure will be essential to discovering or identifying the undoubted other Au-tetradymite deposits in this con- tinental region.
Jul.Aug.Sep 2024 • TPG 15
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56
