Distribution of oxygen isotope values in the Bonito Lake stock and surrounding area, Lincoln County, New Mexico
James Constantopoulos

Abstract:

The Bonito Lake and Rialto stocks are two of the intrusions associated with the Sierra Blanca Volcanics in the Sierra Blanca region of New Mexico. This work, along with previous work in the area, has shown that isotopically-light meteoric water was the dominant fluid responsible for the mineralization and hydrothermal alteration of the volcanic and plutonic rocks in the Sierra Blanca region. Hydrothermal alteration of the stocks and the volcanics is widespread and ranges in intensity from mild to strong and is reflected in depleted oxygen isotope values relative to “normal” isotopic values. Whole-rock δ18O values for the Bonito Lake stock range from 2.0 to 8.4‰ with a mean of 5.3 ±1.9‰ and 3.4 to 5.6‰ for the Rialto stock with a mean of 4.3 ±0.9‰. Oxygen isotope values for the Sierra Blanca Volcanics in the vicinity of the Bonito Lake and Rialto stocks range from 1.0 to 8.0‰ with a mean of 4.2 ±2.0‰. Quartz from gold veins located in the vicinity of the stocks yielded values of 4.9 to 15.3‰ with a mean of 10 ±2.9‰. Isotopic lows in the vicinity of the Bonito Lake stock are, in general, coincident with the location of mineralization in the this part of the Nogal-Bonito mining district. Water/rock ratios were likely low, ranging from less than one up to a high of 2.3. High δ18O values for two Bonito Lake stock samples (8.1 and 8.4‰) are probably due to retrograde interaction with cool meteoric water at low water/rock ratios. A sample of the Sierra Blanca Volcanics collected in the vicinity of vein gold mineralization and containing void-filling quartz and calcite yielded a high value of 8.0‰.


Citation:

  1. Constantopoulos, James, 2014, Distribution of oxygen isotope values in the Bonito Lake stock and surrounding area, Lincoln County, New Mexico, in: Geology of the Sacramento Mountains region, Rawling, Geoffrey; McLemore, Virginia T.; Timmons, Stacy; Dunbar, Nelia, New Mexico Geological Society, Guidebook, 65th Field Conference, pp. 179-182.

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