| Basis for focus area |
Porphyry Molybdenum, Lithocap Alunite (also Polymetallic Vein and Replacement, Lithocap Kaolinite, Volcanogenic Uranium, Fluorspar, Rhyolite hosted Be and Sn). This area includes Pine Grove Mo porphyry to the northwest, White Mountain alunite area to the east, Broken Ridge Sn-Ta to the south, and Indian Peak altered area to the west. Possibly byproduct W, Sn, Nb, REE, from Mo resources and Ga from alunite resources. Outlines from Krahulec (2018b). |
| Identified resources |
Identified aluminum (alunite), molybdenum, and potash (K2SO4) resources; historical production of aluminum (kaolin), beryllium (gemstone beryl), fluorite, lead, molybdenum, silver, uranium, and zinc. |
| Production |
Minor production from polymetallic replacement and vein deposits at Pine Grove. Modest production of U and F at Staats mine near Blawn Mountain. Recently active lithocap kaolinite mine and gem ruby beryl mine near Blawn Mountain. Potash from alunite evaluation (drilling) underway at Blawn Wash. |
| Status |
Past mining. Development drilling at Pine Grove and Blawn Mountain has defined a large molybdenum resource and the country's largest alunite resource. Limited drilling of PV alunite deposit in Broken Ridge district. |
| Estimated resources |
Blawn Mountain. is the largest alunite resource in the U.S. (Hall, 1978) with a Measured + Indicated resource of 812 Mt ore, 153 Mt of alunite = 77 Mt Al2O3 and 32 Mt K2SO4 (Kerr and others, 2017). Pine Grove is a significant Mo resource with 125 Mt at 0.17% Mo (Keith and others 1993). |
| Geologic maps |
Abbott and others (1983), scale 1:24,000; Lindsey and Osmonson (1978), scale 1:24,000; Hofstra (1984), various scales; Haymond (1981), scale 1:24,000; Best and others (1987), scale 1:50,000; Hintze and others (2017), scale 1:50,000; Best and others (1989), scale 1:50,000. |
| Geophysical data |
Inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
Miocene, bimodal rift-related magmatism of 2 ages: ~ 22-18 Ma at Pine Grove and Blawn Mountain and ~ 12 Ma at Broken Ridge. Multiple topaz rhyolite volcanic centers enriched in F, Li, Be, Mo, Sn, Rb, Nb above an inferred granite pluton. Blue Ribbon Lineament in the Pioche-Marysvale mineral belt = crustal structure. |
| Deposits |
Pine Grove (MRDS dep_ids: 10178769, 10042325), Wah Wah mine (Tasso mine; MRDS dep_id: 10276097), Pine Grove Summit prospect (MRDS dep_id: 10042324), Earth Science Alunite deposit (MRDS dep_id: 10010707, 10227548), Staats mine (MRDS dep_id: 10020440), Blawn Mountain (also known as NG Alunite Area). |
| Evidence from mineral occurrences |
MRDS. |
| Geochemical evidence |
Molybdenum anomaly in pebble dike at Pine Grove. Anomalous Mo in rocks near center of Blawn Mountain altered area (Hofstra, 1984). Anomalous Be, F, Sn, Nb, Mo, Cu, Zn, W, and Ba in altered rocks at Broken ridge (cassiterite in panned concentrates) (Duttweiler and Griffitts, 1989). Veinlets with 6 to 13% Mn reported from the Black Jack Skougard mine, and rhodochrosite is present at other mines in the focus area. Gallium occurrences reported in association with Sn prospects. |
| Geophysical evidence |
ASTER alteration mineral maps of the area (Rockwell, 2012). |
| Evidence from other sources |
Blawn Mountain. NI 43-101 technical report by Kerr and others (2017). |
| Comments |
Miocene high silica rhyolite porphyry magmatic centers. Large concealed porphyry Mo resource at Pine Grove. Large exposed lithocap alunite resource at Blawn Mountain. Appears to be a porphyry cluster above a large pluton. A few occurrences and prospects contain cinnabar. Enrichment of Sb, As, Ge, In, Re, and Sc inferred from the mineral system/deposit type table (Hofstra and Kreiner, 2020). |
| Cover thickness and description |
A porphyry Mo deposit may be present below the lithocap alunite deposit at Blawn Mountain and possibly below White Mountain and Broken Ridge. Concealed lithocap alunite may be present below younger mafic volcanic rocks and valley fill between Blawn Mountain and White Mountain. to the east. Undiscovered polymetallic replacement deposits may be present at Pine Grove and below volcanic rocks at Blawn Mountain and White Mountain. Broken Ridge contains veinlets with Sn, and Ta-Nb. |
| Authors |
Albert H. Hofstra, Andrew Rupke, Stephanie Mills, Joshua M. Rosera. |
| New data needs |
Regional aeromagnetics survey; regional map synthesis; multi-element geochemistry of molybdenum ore, alunite ore, ± other deposit types in the area; airborne hyperspectral. |
| Geologic mapping and modeling needs |
Synthesize 1:24,000 scale maps of area and fill in gaps. Possible detailed alteration mapping. |
| Geophysical survey and modeling needs |
Needs Rank 1 aeromagnetics to map concealed intrusions, structures, magnetite destructive alteration and Rank 1 aeroradiometrics to map K-bearing rhyolites, alunite alteration and volcanogenic uranium. Resistivity to map kaolinite and sulfides. Krahulec recommends an induced polarization survey at Blawn Mountain to detect deep Mo porphyry. |
| Digital elevation data needs |
Lidar inadequate. |
