1893 to 1943
The Central Montana Alkaline Province received a fair amount of gold exploration in the 1890s, with the first discovery in the North Moccasins about 1893. Little production from the prospects in the mountain range was completed till the early 1900s, when vat leaching cyanide was introduced into the milling circuits. The mining and milling was restricted to the east flank of the mountain in the Kendall Mining District. Total production from the district between 1893 and 1922 reportedly reached 450,000 ounces of gold and 46,500 ounces of silver. There was only intermittent production till 1943 yet the Kendall District was overwhelmingly the largest producer in all of Fergus County. The total for the entire North Moccasin region is estimated to be 2,133,772 tons of ore averaging 0.238 Au oz/ton and 0.024 Ag oz/ton. These values are attributed to mining along the strike and down dip eastward along the Madison Limestone and syenite porphyry contact. This zone of economic contact mineralization included the Kendall, Barnes King, Muleshoe and Horseshoe mines that are located along a strike length of 9,000 feet.
1960 to 1993
A list of companies that evaluated the perimeter of the North Moccasin gold mines along the intrusive and limestone contact includes:
-Duval Corporation – 1968;
-Golden Cycle – 1971;
-GeoSurveys – 1972 – 1976;
-Coastal Mining Company – 1976 – 1977;
-Gold Fields – 1979 – 1982; and
-Canyon Resources and Kendall Mining began a JV mining program on the old Judith Gold property in 1987 and continued till 1997.
Mine production came from the gold deposits in the karst sinkhole system of the Kendall-type gold deposits that contained Tertiary hydrothermal brecciation introduced along pre-existing fracture zones. The introduction of the Merrill-Crowe processing plant technology greatly improved the recovery of the micron size gold. It should be noted here that no native gold was found within the deposits mined.
1979 to 1993
The Tertiary gold mineralization in the sub-alkalic to alkalic intrusive complex exposed in the core area of the North Moccasin Mountains uplift resulted in an estimated $3.5 million dollars (2012 dollars) being expended on gold exploration between 1979 to 1993. This period of activity was completed by:
-Rexcon Incorporated 1979 -1980;
-H&R Properties 1981 – 1982 (Hecla/Rexcon JV);
-Utah International 1984 -1985;
-Cominco American Resources 1987 – 1989; and
-CR Kendall/Cominco American Joint Venture 1989 – 1993
GOLDEN PLUM / NORTH MOCCASIN - Montana
History and Previous Exploration/Development Efforts
The Golden Plum property is located in the North Moccasin Mountains, Fergus County, Montana, near Lewistown. The property consists of 36 unpatented claims (720 acres).
The North Moccasin Mountains is another isolated, laccolith-type mountain range within the Central Montana Alkalic Province. A substantial felsic laccolithic intrusion produced a domed structure approximately 6 miles in diameter and over 7,000 feet in altitude. Erosion of the uplifted, thick sequence of Cambrian to Tertiary sedimentary and volcanic rocks formed the current altitudes within the 3-½ mile diameter core of that range from 4,600 feet to 5,800 feet and reflects the erosion of approximately 1,700 feet from the exposed dome of the laccolith core. The base of the laccolith is not exposed; however, the incidence of a Cambrian Flathead quartzite inlier suggests a complex basal geometry.
Over several years of state-of-the-art gold-silver exploration in the igneous core of the North Moccasins Mountains has identified at least 5 separate areas of interest that have received specific exploration attention. Syenite to quartz latite porphyries comprise the major rock types within the intrusive core, which is also cut by several breccia pipes, tuff-filled vents, brittle zones or crackle breccia zones and major, north, northwest, and northeast trending structures. A number of radial faults and ring structures cut the flanking areas outside the sedimentary-intrusive contact on the dome. All of the rock types and superimposed structure are intimately related to the late Tertiary gold mineralization. Many dikes, sills and plugs intrude the core and the bounding sedimentary rock units.
Proposed Future Exploration – Phase I
Due to much better understanding of the structural influence on the host rocks of the gold mineralization indicates that there is a possibility of developing a large, high grade vein system deeper in the igneous core of the Golden Plum property. It is strongly recommended that deep probe geophysical methods be used to evaluate the subsurface. There are newly developed geophysical instruments that combine the use of induced polarization to investigate sulfide mineral content and passive magnetotelluric sounding to map geologic units by their resistivity contrasts. This deep-probe IP is capable of imaging to +/- 5,500 ft depth during the day and followed by use of magnetotelluric work accomplished at night. The result is presented as a three dimensional model of this 24 hour procedure.
Completion of 4 or 5, two-mile long lines on a 9 square mile grids would cover all of the most interesting structurally controlled surface gold mineralization on the property.
Additional surface exploration should be considered during the recommended subsurface program. Prior to implementation of the deep probe survey the traverse lines must be established by AMCOR. This will entail clearing and establishing 5 to 7, 10,000 foot lines with location stakes every 100 feet. From 9 miles to 13 miles of deep probe traverse lines would be established. Our objective, subject to securing additional capital, of which there is no assurance would be use the lines to further define the geology and collect additional rock and soil samples in areas not previously explored in the North Moccasin intrusive core. The established and surveyed traverse lines will also make sighting of future drill holes accessible considering use of the existing road network.
Work in the five specific areas presently outlined as targets should be prioritized and further evaluation completed along the following guide lines for comparison to the deep probe survey: Plum Creek Vent, Plum 40 Breccia Pipe, Quartz Ridge Breccia Pipe & Iron Gulch area.
History and Previous Exploration/Development Efforts
All of the exploration in the uplifted mountain core was oriented toward establishing bulk minable gold deposits. Primary targets were a number of crosscutting volcanic vents identified within the intrusive core. AMCOR’s interest in the North Moccasins in 2012 is due to the increased price of gold and silver, combined with the availability of historical technical and scientific data avail to us.
In 1981, the property was drilled on a Joint Venture basis between H & R Properties and Hecla Mining Company (Rexcon Joint Venture). The drilling program consisted of 15,000 ft and assaying was done every five feet. The diamond drilling program resulted in the discovery of several strong gold-mineralized zones; 1) 40 ft of 0.174 oz/ton Au; 2) 80 ft of 0.077 oz/ton Au; and 3) 5 feet of 0.95 oz/ton Au. The speculative open pit potential resulting from this initial drilling totaled 1.8 million tons of 0.1 to 0.2 oz/ton Au. The underground potential confined only to vent-filled clastics is estimated at .4 million tons of 0.1 to 0.3 oz/ton Au. At a depth of 2,000’ drilling indicated another potential of 1.0 million tons of 0.1 to 0.5 oz/ton Au. In addition to the mineral zones defined in this early program, there exists an open pit potential of another several million tons in the area referred to as Gold Ridge. In addition to the gold mineralization described above, drilling encountered 340 ft. of 0.005 oz/ton Au and a 100 ft. zone of 0.019 oz/ton Au. There exits the potential for a large stratabound vent-filled deposition at the Plum Gold property. Previous drilling by H & R Properties and Hecla Mining Company also defined a potential molybdenum reserve estimated up to 5.0 million tons of 0.1 to 0.5% Mo at a depth of 500 ft under Heller Ridge.