WYOMING STATE GEOLOGICAL SURVEY Ronald C. Surdam, State Geologist GUIDE TO PROSPECTING AND ROCK HUNTING IN WYOMING by W. Dan Hausel Information Pamphlet 11 LARAMIE, WYOMING 2004 WYOMING STATE GEOLOGICAL SURVEY Ronald C. Surdam, State Geologist GEOLOGICAL SURVEY BOARD Ex Officio Dave Freudenthal, Governor Randi S. Martinsen, University of Wyoming Don J. Likwartz, Oil and Gas Supervisor Ronald C. Surdam, State Geologist Appointed Ronald A. Baugh, Casper Gordon G. Marla�, Laramie John P. Simons, Cheyenne John E. Trummel, Gille�e Wallace L. Ulrich, Moose STAFF Computer Services Unit Publications Section Jesse T. Bowen - Manager Richard W. Jones - Editor/Senior Staff Geologist Jaime R. Moulton- Assistant Editor Geologic Sections Nancy S. Ellio� - Sales Manager James C. Case, Senior Staff Geologist - Geologic Hazards Phyllis A. Ranz - GIS Specialist/Cartographer Rodney H. De Bruin, Senior Staff Geologist - Oil and Joseph M. Huss - GIS Coordinator Gas Ray E. Harris, Senior Staff Geologist - Industrial Minerals Laboratory Unit and Uranium Robert W. Gregory - Laboratory Technician W. Dan Hausel, Senior Economic Geologist - Metals and Precious Stones Supportive Services Unit Robert M. Lyman, Staff Geologist - Coal Susanne G. Bruhnke - Office Manager Alan J. Ver Ploeg, Senior Staff Geologist - Geologic Joan E. Binder - Administrative Assistant Mapping This and other publications available from: Wyoming State Geological Survey P.O. Box 1347 Laramie, WY 82073-1347 Phone: (307) 766-2286 Fax: (307) 766-2605 Email: [email protected] Web Page: h�p://wsgsweb.uwyo.edu People with disabilities who require an alternative form of communication in order to use this publica- tion should contact the Editor, Wyoming State Geological Survey at (307) 766-2286. TTY Relay operator 1(800) 877-9975. Front cover: This 34-ounce gold nugget was reportedly found at South Pass, Wyoming, during a past gold rush. The nugget measures about 2 1/2 inches across and includes some chalcedony nodules. Several large nuggets have been found at South Pass, including one boulder that reportedly contained as much as 630 ounces of gold (see Hausel, 1991). Photograph courtesy of the Natural History Museum of Los Angeles County, Los Angeles, California. INTRODUCTION Welcome to Wyoming! If you have come to our state to search for gold, diamonds, agates, or other precious metals or gemstones, you will find there is a wonderful opportunity to prospect or rock hound in the Cowboy State. Wyoming contains a large variety of minerals and rocks, and new discoveries are made every year. Many people are under the erroneous impression that every- thing has already been found in the state, when in fact several gem- stone and gold discoveries have been made in Wyoming during the past few decades. For instance, diamonds were accidentally discovered in 1975 south of Laramie and since then a number of diamond-bearing deposits have been identified in Wyoming and Colorado. More than 130,000 diamonds (including gems weighing more than 28 carats) have been recovered along the Colorado-Wyo- ming border south of Laramie. Geological and mineralogical evi- dence indicates that many more diamond discoveries will be made in the future. Some gold was also found in Wyoming in recent years. One of the most impressive finds during the past 50 years was the author’s 1981 discovery of an entire gold district west of Casper in the Ra�lesnake Hills area (Hausel, 1998) (Figure 1). Following this discovery, some major mining companies and private consultants explored the district and located several other gold anomalies that led to drilling a significant, large-tonnage, low-grade gold resource at Sandy Mountain. There may be as much as 1 million ounces of gold at that site (Miller, 1999). Several other gold discoveries were made by the Metals and Precious Stones Section at the Wyoming State Geological Survey (WSGS) during mapping projects in the historic mining districts at South Pass (Hausel, 1991), Seminoe Mountains (Hausel, 1994), Sierra Madre (Hausel, 1986), and Medicine Bow Mountains (Hausel, 1989; 1993) (Figure 2). In addition to the above lode discoveries, pros- pectors and treasure hunters have found many gold nuggets near some of these lodes with the use of metal detectors. A 7.5-ounce nugget was found at South Pass by a Wyoming prospector. Another treasure hunter from Fort Collins, Colorado found more than 100 nuggets at South Pass, and a prospector from Arizona recovered 399 nuggets in the Sierra Madre (Hausel and Sutherland, 2000). 1 R. 88 W. R. 89 W. 2 Aut 1 Tph 6 EXPLANATION D U Aut VOLCANIC ROCKS Tph Tph Aut SEDIMENTARY ROCKS dt Tsr Split Rock Formation Tph Aut Tat Phonolite Tat Tat Alkali meta-trachyte Aut Tph Tc Boulder conglomerate Tst Soda trachyte 1/2 0 Twb Wagon Bed Formation Tt Trachyte Twb Tph 1 1 mile Tl Latite 12 Tql Quartz Latite 11 1/21 0 1 kilometer Aut Tph 7 mg mg Tph INTRUSIVE METAIGNEOUS ROCKS Twb Aut mg Metagabbro Twb Aut Tph dt Tonalite Tt Tph Tph Tph mg Tph gr Granodiorite ap Aplite Twb Twb UT CREEK FORMATION Tph Asb mg 14 mg Aut mg Asb Metabasalt mg 13 Asb 18 Aut Aut 16 Aut Metagreywacke Twb mg Aut 15 mg 17 Tc mg Tph Tst mg Twb McDOUGAL GULCH METAVOLCANICS Aut Tph Tst Aut gr mg mg ap Amb Metabasalt and ultramafic schist Asb mg Tl Tph mg Tc ap BARLOW SPRINGS FORMATION Aut Twb Tl Asb Aut Tl Tst Goat Sandy Mtn. mg Asb Bmb Metabasalt, banded iron formation, Tl Tph Twb mg Asb Lost Muffler quartzite, pelitic schist; metafelsite, and 2 Mountain Tph Tt Asb adit tremolite-chlorite schist. Tph Tph Tc 20 21 22 23 GRANITE GNEISS COMPLEX 23 24 Tst 19 mg Aut Aut Aut Tst LOST MUFFLER FAULT Gu Undifferentiated granitoids, gneissic mg Tst breccia, granite, felsic gneiss, and Twb Tc amphibolite gneiss. Tl Amb mg Twb Twb U mg Fault UT CREEK FAULT D Tl Aut Tst Oshihan Hill Tph Twb Bmb Twb mg mg Amb Amb Aut Tql Tql Tph 26 Tsr U Tsr 28 Tst 27 26 Twb mg Bmb D 29 Tsr Tql 25 Gu 25 30 Aut Tsr Tsr Tph Aut COTTONWOOD CREEK FAULT Aut Twb Tsr U Gu Aut D 32 Tsr 31 33 Tsr 36 35 36 34 35 Tsr T. Tsr U 32 D N. Figure 1. Generalized geologic map of the Rattlesnake Hills gold district (from Hausel, 1996b). 111 110 109 108 107 106 105 104 45 45 Beartooth EXPLANATION Mountains NEW WORLD BALD MOUNTAIN (COOKE CITY) Eocene Absaroka Sheridan Volcanic Supergroup BIG CROOK SUNLIGHT WALKER MOUNTAIN CAMPBELL YELLOWSTONE HORN SHERIDAN Tertiary intrusive rocks NATIONAL Black PARK Absaroka Cody BEAR LODGE Hills Greybull MOUNTAINS uplift Precambrian igneous EAGLE Bighorn Bighorn and metamorphic rocks CLOUDS HOME GOOSE Sundance CREEK Volcanic PEAK PORPHYRY Buffalo PORPHYRY CREEK MINERAL HILL PARK Basin Mountains Mullen Creek – Plateau KELLY CREEK Gillette Nash Fork Shear Zone DEER CREEK PORPHYRY BLACK ROBINSON CREEK Mineralization STINKINGWATER HAZLETON BUTTES 44 PORPHYRY Worland PEAK Powder KIRWIN Teton WASHAKIE Range Jackson JOHNSON River Newcastle Hole HOT SPRINGS WESTON Thermopolis TETON Owl Basin Creek-Bridger Bighorn Gros Jackson Mountains Ventre COPPER Mountains Range Hoback MOUNTAIN Basin FREMONT NATRONA CONVERSE NIOBRARA Wind Casper 43 River arch Wind Riverton 3 Basin MUSKRAT Pinedale RATTLESNAKE CANYON River Lander Casper DEER HILLS CREEK Lusk Range Douglas TIN CUP CASPER LaPRELE RAWHIDE SUBLETTE MOUNTAIN BUTTES ESTERBROOK Granite Hartville WILDCAT LAKE ALICE Shirley uplift HILLS Mountains Basin McCANN Green PLATTE PASS SOUTH PASS WARBONNET LINCOLN GREENSTONE BELT MINERS Laramie HAYSTACK River CANYON RANGE SEMINOE Mountains Wheatland 42 Great Divide MOUNTAINS Hanna Torrington Basin IRON MTN. ELMERS ROCK Basin CARBON Basin GREENSTONE Kemmerer TITANIFEROUS MAGNETITE BELT Moxa Rock ALBANY arch LEUCITE HILLS Rawlins ELK LAPLATA IRON MTN.GOSHEN Overthrust Belt Springs LAMPROITES MOUNTAIN COOPER KIMBERLITES Rock Springs NEW RAMBLER GOLD HILL STRONG Green River uplift MINE HILL Laramie MINE Denver- UINTA KIMBERLITE BIG CREEK Basin Cheyenne INDICATOR CENTENNIAL SWEETWATER RIDGE Laramie Basin Evanston MINERALS Washakie Medicine SILVER NORTH Basin KEYSTONE CROWN SCALE ENCAMPMENT Sierra LAKE CREEK 0 Bow Cheyenne 10 20 30 40 50 Miles JELM MTN. LARAMIE 41 Madre Mts. COPPER STATE LINE 41 RIDGE 111 104 Figure 2. Principal mineralized regions and mining districts in Wyoming (modified from Hausel, 1997). Besides gold and diamonds, other metals and gemstones are also found in Wyoming. In 1995, a significant platinum, palladium, and nickel anomaly was identified in the Puzzler Hill area of the Sierra Madre near Saratoga (Hausel, 1997; 2000a). A few other areas in southeastern Wyoming also have the potential for discovery of platinum-group metal deposits. Wyoming was known for its spectacular jade finds in the 1930s and 1950s, but in more recent years, other gemstones have been found. One of these was a beautiful, 1- to 2-foot long aquamarine from the Anderson Ridge area found by a prospector from Lander. In 1998, approximately 13,000 carats of gem-quality peridot and industrial olivine were recovered from two anthills near Black Rock in the Leucite Hills north of Rock Springs. Another a�ractive gemstone, known as iolite (gem-quality cordierite) was also found in 1998. This gem is transparent and changes from sapphire-blue to violet-blue depending on the direction from which it is viewed (Hausel and Sutherland, 2000). A group of iolite specimens weigh- ing more than 1000 carats has been recovered by the WSGS. Some rubies and sapphires have also been found in the state. So kick a few rocks around and keep your eyes open—you may find a new mineral deposit or occurrence, maybe even a whole new district! History of prospecting The first prospectors in Wyoming were looking for gold. Span- iards may have found gold more than 200 years ago, but historical records indicate that gold was initially discovered in 1842.