West Butte
Photo by John Smart of Helena, Mt.(Taken from Chapter 3 of the Final Amendment and Enviornmental Impact Statement, April 1996)
The study area is classified as having high occurrence potential and moderate development potential for precious metal deposits. These deposits are associated with igneous intrusions that originated at depth and moved up through the earth's crust before cooling near the surface. Precious metal deposits are considered locatable under the provisions of the 1872 mining law on Federal land... The following discussion applies to these deposits in the Sweet Grass Hills.
West Butte
Photo by John Smart of Helena, Mt.
The Sweet Grass Hills consist of three separate butte complexes, East, Middle and West Buttes, and two smaller features, Grassy and Haystack Buttes. The Sweet Grass Hills consist of igneous intrusive rocks that are considered Eocene in age (Ross, 1950). These igneous rocks range in composition from shonkinite to syenite to intrusive trachyte with a minor amount of lamprophyre. The surrounding sedimentary rocks domed up by the intrusives range in age from Mississippian to Cretaceous. These are primarily limestones and shales with minor amounts of sandstone. The older Mississippian Madison Formation occurs near the central portions of East and West Buttes, and the younger Jurassic-Cretaceous formations are found adjacent to Middle Butte, which is of smaller size. The sedimentary rocks, particularly limestone, have been chemically and physically altered due to contact metamorphism and hydrothermal fluids associated with the igneous activity.
Middle (Gold) Butte John Smart
PhotoThe Sweet Grass Hills are prominent land marks, rising nearly 3,000 feet above the surrounding plains and are visible for more than 50 miles. West Butte lies 13 miles west-northwest of Whitlash, the nearest town. The central core is an exposure of diorite porphry and monzonite, a rock similar to common variety granite, but with less quartz. Middle Butte lies 3 miles west-southwest of Whitlash and covers a hilly area about 5 miles wide and 5 miles long. The ghost town of Gold Butte, formerly a gold mining camp, rests on the northwest flank of the tallest hill in the Middle Butte complex, which bears the same name as the former town. Gold Butte is an exposed laccolith consisting of diorite porphry. It is separated from two other buttes, of similar composition, by carbonaceous shale which is cut by numerous dikes and sills. The sedimentary rocks are less resistant and form swales between the higher ridges composed of igneous rock. East Butte consists of alkalic igneous rocks intruding Paleozoic and Mesozoic sedimentary rocks as plugs, laccoliths, stocks, dikes, and sills. The igneous rocks consist of monzonitic and syenitic trachytes and latite porphyries. The domed sedimentary rocks are silicified, altered and highly fractured. Limestone alteration includes recrystallization as marble and some skarn mineralization. Quartz with pyrite, magnetite, and fluorite mineralization also occur primarily as fracture filling in places (Gavin, 1991). The Jurassic and Cretaceous rocks composed primarily of shales and fine siltsones show signs of contact metamorphism ranging from recrystallization to silicification and intense fracturing. East Butte is the largest of the 3 Buttes with a 9 square mile area of uplifted terrain. The combination of igneous intrusive rock and altered sedimentary strata has not been mapped in enough detail to differentiate between the separate sedimentary units. Much of the valley bottoms and the lower slopes of ridges are covered with Quaternary alluvium and colluvium. This makes interpretation through surface mapping more difficult.
John Smart Photo East Butte 
Devil's Chimney Cave, in East Butte, is a roughly circular solution cavity, or room, within the limestone formation. The room is about 50-feet across with a 10-foot diameter opening to the surface 40 feet above the cave floor. No speleothems were observed inside the cave (Campbell, 1978). There is a large amount of break-down material on the cave floor. Montana State University (MSU) conducted preliminary investigations of less than one-half of one percent of the cave break-down deposits in the early 1970s. Numerous faunal remains, some of which exhibited modification, were recovered during the excavations. The exploratory testing conducted by MSU established the fact that Devil's Chimney cave does contain Holocene faunal remains. The cave has the potential to contribute important information to the paleo-environmental record on the northern plains.
Economic Geology
Historical Activity: A small amount of gold was recovered from placer operations in Two Bit Gulch on the north slope of Gold Butte within the Middle Butte complex in 1883 (for futher details click here). The total yield of placers near Gold Butte is probably less than 2,000 ounces of gold (Ross, 1947). Lode deposits at the head of Ribbon Gulch, in the East Butte complex, were reported at about 8,700 pounds of copper, 8,400 pounds of lead, 1,100 pounds of zinc, and 651 fine ounces of silver. This activity was reported from underground exploration at the Sweetgrass Mine in 1963 (Hubbard, 1966). The area was explored for copper, lead, zinc and silver by the Anaconda Copper Company during the late 50s and early 60s. This included drilling on lode claims on all three buttes. The East Butte vein deposits were the only claims that justified underground excavation and sampling of ore in addition to the drilling. The mine portal location is shown on the south side of Mount Royal.
Recent gold exploration in the East Butte area (1986-Santa Fe Pacific Mining, Inc. and 1989-Cominco American Resources) after 20 years of relative inactivity is the result of two main factors. First, the technology of heap leach mining methods which allowed economic recovery of fine gold from low grade deposits using cyanide solution percolated through high volumes of ore was successfully used at other mines in central Montana.
East Butte of the Sweetgrass
Hills John Smart
Photo
Location threatend by existing mining claims not included in 20 year withdrawal
Second, the deregulation of gold prices in 1974 placed new emphasis on exploration in areas with known reserves. The price of gold went from $35 an ounce to $800 an ounce by 1980, and has remained fairly constant in the $300 to $400 an ounce range over the last decade. The higher prices have resulted in a rejuvenation of gold mining activity throughout the western states. Many areas passed over during the late 1880s and early 1900 mining era are being evaluated for development at the current higher prices.
There are many factors that figure into the equation before a decision to invest in the development of a mine. These include; the size of the deposit, metallurgy of the gold mineralization, mining, crushing and hauling of the ore and waste, permitting costs, and proximity to sources of equipment and supplies. The Sweet Grass Hills, unlike other areas of recent mining activity, have no history of productive gold mines. This may be an indication that the more conventional lode deposits do not exist or are not as readily apparent and that the recent exploration is the first venture into defining disseminated gold deposits in the Gold Butte mining district.
Recent Activity: To date, mining activity on Federal lands within the Sweet Grass Hills resulted in the construction of 20,000 feet of access roads and drilling nine exploration holes in the Tootsie Creek area of East Butte. All of the holes were plugged and the roads backsloped and reseeded. This activity was approved by the BLM and DSL under two separate Plans of Operation. The exploration was conducted by two companies in a joint venture with the claimant. In addition to the drilling data the companies sampled and mapped the bedrock exposed in the road cut. The metals sampled for include; molybdenum, copper, lead, zinc, silver, nickel, arsenic, cadmium, antimony and gold. Soil and stream geochemical sample analysis was also conducted.
Extensive mapping and rock sampling has been conducted in the Breed Creek and Tootsie Creek area of East Butte. Data sources show widespread mineralization and positive precious and base metal anomalies exist in these areas. The Tootsie Creek area is the most well defined area in East Butte. Ten years of exploration at Tootsie Creek has produced 4,200 feet of subsurface information from 14 drill holes which includes over 800 assays, and over 11,000 feet of surface-trench samples with over 1,250 assays. Scores of outcrop data and hundreds of geochemical soil assays are also on file. Reports summarizing the results of the sample analysis at Breed Creek and Tootsie Creek have been submitted to the BLM for use in resource assessment.
The most current proposed exploration activity is an exploration plan submitted by Manhattan Minerals (US) Ltd. to the BLM and DSL in February 1992. A draft Royal East Joint Venture Exploration Project Environmental Impact Statement (EIS) was issued on this proposal in January of 1993 which describes this proposed activity. The reader is referred to that EIS for more information on the proposal.
The BLM has completed the validity examination of E.K. Lehmann's 14 unpatented mining claims on the East Butte. The results indicate eight of the claims meet the test of discovery under the mining law and are valid (Figure 2). The validity examination process determines if there is sufficient showing of a mineral to constitute a discovery, which in turn justifies a prudent person spending money with a reasonable prospect of success.
In addition to the exploration on East Butte, Montana Gold Butte Mining is currently conducting underground mining/sampling in the Middle Butte area on private land (personal communication with Pete Strasdas, DSL). No data is available on the results of this activity. It is a small operation permitted for removal of less than 36,500 tons per year. A placer mining operation is located on the northwest side of Middle Butte in the headwaters of Eclipse creek. Surface flow in the area is intermittent and availability of water restricts the operation to springtime seasonal use. There is no data available on production from this operation. West Butte has been the site of recent exploration in the form of surface mapping and soil geochemical sampling on unpatented claims. Currently no application for drilling or trenching has been received by the BLM and DEQ in this area.