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Avalon Placer (Onondaga; Syracuse; Silver Str.), Boulder Co., Colorado, USA

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Latitude & Longitude (WGS84): 39° 56' 46'' North , 105° 39' 26'' West
Latitude & Longitude (decimal): 39.94622,-105.65724
GeoHash:G#: 9xhg5xyxx
Locality type:Placer
Köppen climate type:Dfc : Subarctic climate


REF:Deposit:: BLM COLO. CONNECTING SHEETS
Deposit:: CONSV. DIV. COMP. DATE, 10,62
Commodities (Major) - Silver, Gold
Development Status: Occurrence


Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.


Mineral List


2 valid minerals.

Regional Geology

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

Late Pleistocene
0.0117 - 0.126 Ma



ID: 2207395
Till of Pinedale age

Age: Pleistocene (0.0117 - 0.126 Ma)

Description: Mostly nonsorted and nonstratified, subangular to subrounded boulders to granules in a silty sand matrix. Material less than 2 mm in diameter is estimated to be 20–40 percent of unit. This material consists chiefly of poorly sorted sand and ≤20 percent silt and ≤5 percent clay. Unit commonly forms large prominent, sharp-crested lateral and end moraines that are very bouldery and have distinct constructional morphology. Deposits in some areas have well-expressed knob-and-kettle topography. Surface soils have A/Cox profiles on moraines with narrow crests and A/Bw/Cox and A/Btj/Cox profiles on moraines with broad crests. Surface and near-surface O and E soil horizons are locally present. Cambic (Bw) and weak argillic (Btj) horizons are thin (10–40 cm) and commonly contain 1–5 percent more clay than the underlying till (<2 mm size fraction). Most of the biotite-rich granitic and gneissic clasts within the soil are unweathered, and disintegrated clasts are rare. Unit locally includes deposits of stratified drift, mass-movement and glacial deposits, undivided (Qmg), tills of the Satanta Peak and Triple Lakes advances of Benedict (1985), about 12–10 ka (Davis, 1988), till of Bull Lake age (Qtb), colluvium (Qc) and other mass-movement deposits, and valley-floor alluvium (Qva); locally may include till of pre-Bull Lake age. Radiocarbon (14C) and cosmogenic-exposure ages indicate that till of unit Qtp is about 30–12 ka (Nelson and others, 1979; Madole, 1986; Schildgen and Dethier, 2000; Benson and others, 2004, 2005). Subsurface deposits and locally some surface deposits of unit Qtp may be older than 30 ka, because uranium-series ages of travertine in the northern Yellowstone area suggest an early advance of Pinedale ice about 47–34 ka (Sturchio and others, 1994). Estimated thickness 1.5–30 m

Reference: Kellogg, K.S., Shroba, R.R., Bryant, Bruce, and Premo, W.R. Geologic Map of the Denver West 30' x 60' Quadrangle, North- Central Colorado. USGS Geologic Investigations Series 3000. [35]

Paleoproterozoic
1600 - 2500 Ma



ID: 2957947
Biotitic gneiss, schist, and migmatite

Age: Proterozoic (1600 - 2500 Ma)

Description: Locally contains minor hornblende gneiss, calc-silicate rock, quartzite, and marble. Derived principally from sedimentary rocks

Lithology: Major:{biotite gneiss,schist,migmatite}, Minor:{gneiss,calc silicate schist,marble}

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. [133]

Paleoproterozoic
1600 - 2500 Ma



ID: 3186950
Paleoproterozoic crystalline metamorphic rocks

Age: Proterozoic (1600 - 2500 Ma)

Lithology: Orthogneiss/paragneiss

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License



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