Engesser Mine (Engesser prospect; Johnnie prospect), Engesser Pass, Tank Mountains District, Tank Mts, Yuma Co., Arizona, USA
|Latitude & Longitude (WGS84):||33° 13' 51'' North , 113° 51' 27'' West|
|Latitude & Longitude (decimal):||33.23083,-113.85750|
|Other regions containing this locality:||Sonoran Desert, North America|
A Au prospect located in the NE¼ sec. 25, T2S, R16W (protracted), on land of unknown status.
Mineralization is varied: (1) Scattered, short, lenticular, and narrow, gold-bearing quartz, carbonate, iron oxide and minor, partly oxidized, copper and iron sulfide veins in fissure zones in Mesozoic granitic intrusive and metamorphic schist, with dioritic to rhyolitic dikes. Wall rocks are sericitized, silicified, and carbonatized. Gold concentrated by weathering in near-surface iron oxides and quartz.
Country rock is granite exhibiting coarse, pinkish phenocrysts of orthoclase and dark minerals, largely chlortized. It is cut by dikes of diorite porphyry & rhyolite porphyry & adjacent to veins, is rather intensely altered to sericite and carbonite. The vein strikes N20E & dips 45W.
Workings include an old, irregular shaft about 300 feet deep along the dip of the vein and a few short, irregular drifts.
9 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
|Tithonian - Toarcian|
145 - 182.7 Ma
|Jurassic granitic rocks|
Age: Jurassic (145 - 182.7 Ma)
Description: Granite to diorite, locally foliated and locally alkalic; includes Triassic(?) granitoids in the Trigo Mountains. This unit includes two dominant assemblages of igneous rocks. The Kitt Peak-Trigo Peaks superunit includes, from oldest to youngest: dark, foliated or gneissic diorite, medium-grained equigranular to porphyritic granodiorite, and small, irregular intrusions of light-colored, fine-grained granite. The Ko Vaya superunit, limited to south-central Arizona, includes texturally heterogeneous K-feldspar-rich granitic rocks. (150-180 Ma)
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. 
Arizona Bureau of Mines Bull. 135 (1933), Arizona Gold Placers & Placering: 23.
Wilson, E.D., Cunningham, J.B., and Butler, G.M. (1934), Arizona Lode Gold Mines and Gold Mining (revised 1967), Arizona Bureau of Mines Bull. 137: 148.
Keith, Stanton B. (1978) State of Arizona Bureau of Geology and Mineral Technology, Geological Survey Branch Bull. 192, Index of Mining Properties in Yuma County, Arizona: 179 (Table 4).
Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd. ed.: 262.
U.S. Bureau of Mines file data.
MRDS database Dep. ID file #10162352, MAS ID #0040271055.