Altered igneous rocks around Rocky Mountain manto deposits: the Gilman (Colorado) example

Conference · Tue Jan 01 00:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6196534

O'Neill, T F; Merchant, J S; Beaty, D W; Whitney, G

The Pando Porphyry at Gilman, Colorado forms an easterly-dipping sill above a major manto sulfide ore deposit hosted in the Leadville Dolomite. The sill is regionally altered to a propylitic assemblage (chl-epid-carb). Above the ore bodies the base of the sill is regionally altered to a phyllic assemblage (2M mica-qtz-py-kaol). The phyllic zone is divisible using birefringence of 2M mica into three subzones, which are mineralogically identical and gradational into one another. The phyllic zone is surrounded by a kaolinite-rich argillic zone with local sparse smectite. Spatially, the phyllic alteration is closely confined to the area of the ore bodies. Moreover, the thickness of phyllically altered porphyry is directly correlated with the intensity of mineralization. The distribution of alteration in the Pando sill (age = 70 Ma) requires that the manto mineralization process was at least predominantly: 1) hydrothermal; 2) Tertiary in age; and 3) had up-dip hydrothermal flux along the base of the sill. The sequence propyllitic-argillic-phyllic-ore is present at several other large Rocky Mountain manto deposits and argues for an epigenetic origin involving high-T, low-pH fluids.

• Research Organization: Camino Viviente, Goleta, CA (USA)
• OSTI ID: 6196534
• Report Number(s): CONF-8510489-
• Journal Information: Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
COLORADO
PLUTONIC ROCKS
HYDROTHERMAL ALTERATION
MINERALIZATION
PETROLOGY
GEOLOGIC HISTORY
HYDROTHERMAL SYNTHESIS
METAMORPHISM
MINERALOGY
PETROGENESIS
ROCK-FLUID INTERACTIONS
SULFIDE MINERALS
FEDERAL REGION VIII
GEOLOGY
IGNEOUS ROCKS
MINERALS
NORTH AMERICA
ROCKS
SYNTHESIS
USA
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)