Stevens Exploration Management Corp.

Consulting Geologists and Exploration Contractor
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SEMC Project Summaries

Prospectors working for Leo Mark Anthony staked the Denali Copper prospect in the fall of 1963. I had just started as a geology student at the University of Alaska Fairbanks at that time, but from then on worked each summer I was an undergraduate as a prospector for Mark Anthony. For short periods during the summers of 1964, 1965, and 1966, I worked on the prospect, usually doing pick and shovel work digging trenches.  Then I would be off on other exploration projects for Mark. 

 

In 1967, Doug Colp, a respected mining engineer was hired as the Project Engineer for the exploration program at the Denali Copper prospect, and I was hired as the Project Geologist, having just received my B. S. degree in Geology from UAF. Robert H. (Bob) Seraphim Ph.D., PEng. from Vancouver, B. C. visited the camp about once a month and reviewed our work and made suggestions. I spent most of the summer mapping geology with the aid of a D-6 Cat with a tilt-angle blade on the steep slopes. My strategy was to start with an outcrop with the contact between the volcanic rock and the mineralized sediment exposed and to follow it, wherever it led.  This approach yielded a good geologic map that allowed good targeting of diamond drill holes which was a huge improvement.  During the latter half of the summer we started drilling and had some nice high-grade intercepts of finely-bedded chalcopyrite in carbonaceous limey argillite.

In the spring of 1969, I was hired to be the Project Manager for the summer exploration program which consisted of driving a 1,400 foot adit on the 4,630 level, surface diamond drilling, underground diamond drilling, percussion drilling underground, bulk sampling of the mineralization underground, geologic mapping, and a geochemical survey. I had also received approval for this prospect to be my Ph. D. dissertation project through the University of Alaska Fairbanks and mapped the surrounding area in my spare time. Dave Gaard was my assistant, and the other 26 people in camp were contract miners, diamond drillers, and the cook and his wife. This was a very busy summer, and the project was a success. Based on my work, Owen Kingman, Vice President of Cities Service Minerals Corporation, one of the partners funding the work, offered me the position of District Geologist for Alaska based in Anchorage, AK with Cities Service Minerals upon completion of my dissertation.  I started work as the District Geologist in August, 1970 two days after my dissertation defense.

In 1970, Wayne Murton was Project Manager on the prospect and a spiral decline was driven using Wagner Scooptrams, more diamond drilling, bulk sampling etc. Kingman offered Wayne the position of District Geologist in the Vancouver, B. C. office. Harry Ranspot was the Northern Region manager and we both reported to Harry.

After the 1970 program, a series of reports were written usually by Bacon and Crowhurst in conjunction with Bob Seraphim. Bob calculated that the main ore horizon was about 30 feet thick at its maximum, and contained about 550,000 short tons of 5.84% copper, about 1/3 ounce of silver per ton, and just a trace of gold. Zinc and lead are negligible. Metallurgy was deemed difficult because of the very fine grained nature of the mineralization and that stopped the project.  Modern advances in metallurgy have eliminated this problem.  Note that these calculations are not in compliance with the modern NI 43-101 standard.

The following is the abstract from my dissertation:

The Denali Prospect (147º 08’ 20” W, 63º 08’ 50” N) is located in the Clearwater Mountains of Alaska in the pass between Windy Creek and the South Fork of Pass Creek. A series of stratiform sulfide deposits are intercalated with Upper Triassic andesitic volcanics. Sediments overlying the volcanics and sulfide deposits include argillites, blue-grey and black limestone, black shale, and tuffaceous units. A Jurassic diorite intrusion was emplaced 2500 feet north of the sulfide horizons, causing hornblende hornfels and albite-epidote hornfels facies contact metamorphism. A Paleocene prehnite-pumpellite-quartz facies burial metamorphism has also affected the area. There is no apparent hydrothermal alteration adjacent to the sulfide deposits.

Pyrite and chalcopyrite occur as distinct beds as well as disseminations in black, graphitic, calcareous argillite. The chalcopyrite is extremely fine grained and shows some remobilization. Pyrite occurs as small framboidal aggregates. The sulfides are in planar accumulation parallel to bedding and never crosscut major bedding units.

The sulfur isotope ratio analyses of the sulfides average -28.35‰ which is strongly suggestive of a biogenic origin for the sulfur. However, the standard deviation of eight analyses was only ±1.01‰. Where pyrite and chalcopyrite were in coexistence, the pyrite averaged 1.66 % lighter than the chalcopyrite.

The Denali Prospect stratiform sulfide deposits formed in a euxinic marine basin where abundant organic matter and sulfate reducing bacteria created a strongly reducing environment. The sulfate reduction was unidirectional as chalcopyrite precipitated as the sulfide ion was produced. The stoichiometric excess of iron and sulfide ion was precipitated as pyrite.

 

 

 

Figure 1 Plan view of geology and mineralization.

 

 

Figure 2  Cross section of geology and mineralization.



The citation for the dissertation is:

          Stevens, D. L., 1971, Geology and geochemistry of the Denali Prospect, Clearwater Mountains, Alaska: Unpub. Doctorate dissertation, University of Alaska.

Bob Seraphim published an article in Economic Geology with a little different perspective on the origin of the mineralization:

          Seraphim, R. H., 1975, Denali – A nonmetamorphosed stratiform sulfide deposit: Econ. Geol., v. 70, no. 5, p. 949-960.

Thomas E. Smith, geologist with the Alaska Division of Geological and Geophysical Surveys published a report on the regional geology of the Clearwater Mountains. The link to that publication is at:

          http://www.dggs.dnr.state.ak.us/pubs/pubs?reqtype=citation&ID=406

This excellent summary contains a geologic map of the Healy A-1 quadrangle in which both this prospect and Valdez Creek occur.

This prospect is still available and has considerable exploration potential. The deepest drill hole intersects excellent grade mineralization at a depth of 1,000 feet below outcrop. Subsequent surface exploration by Leo Mark Anthony has extended the known mineralized horizons to the northeast several thousand feet. There are at least four other mineralized horizons that have only shallow drill intercepts.

Logistics are easy. A truck can be driven from Anchorage to the prospect in about 7 hours. The prospect is located about 70 miles from the Alaska Railroad siding in Cantwell, Alaska.  The Denali Highway portion of the trip is about 55 miles, and from the highway to the prospect is about 15 miles by 4 wheel drive only trail.  See the Google Earth view below.  The prospect is at the headwaters of Windy Creek which flows west with its confluence with the Susitna River just north of where the Denali Highway crosses the Susitna River.


Contact me for more information.  The owners now call the prospect Caribou Dome.


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