Geology Reports⌕ Search
Home/Archive/USGS

USGS · 70011215

Isotopic studies of mariposite-bearing rocks from the south- central Mother Lode, California.

R. W. Kistler·F. C. W. Dodge·M.L. Silberman
View original source ↗Export metadata ↓

Abstract

Gold-bearing vein formation in the Mother Lode belt of the study area apparently occurred during the Early Cretaceous between 127 and 108 m.y. B.P. The hydrothermal fluids that carried the gold precipitated quartz and mariposite at approx 320oC, similar to the T of precipitation of gold-bearing quartz veins in the Allegheny district. The O- and H-isotopic composition calculated for the fluid indicate that it was similar to formation water or was metamorphic in origin. If the carbonate in the veins was in isotopic equilibrium with this same fluid, it apparently precipitated at a higher T of approx 400oC. The Sr in the carbonate is much less radiogenic than that in any known marine carbonate, but is similar in isotopic composition to that in metamorphosed mafic volcanic rocks of the general region. These mafic rocks could have been the source for the Sr in the hydrothermal veins. This observation supports the contention that the gold-mariposite-quartz-carbonate rocks were formed as an alteration product of serpentinite and other mafic igneous rocks.-A.P.

Explore related subjects

California GeologyArticle

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

R. W. Kistler, F. C. W. Dodge, M.L. Silberman. 1983. Isotopic studies of mariposite-bearing rocks from the south- central Mother Lode, California.. https://pubs.usgs.gov/publication/70011215

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Helping California get ready for when the mud hits the fan

With frequent wildfires, powerful rainstorms, steep terrain, and dense population, California is particularly vulnerable to postfire hazards like flooding and debris flow. Major postfire flooding and debris-flow events can be more costly than the fire itself, causing dozens of fatalities and widespread damage (Chawner, 1934; Lancaster et al., 2021). Smaller events occur nearly every year in California and can locally damage structures and roads, affect water quality and storage, and result in injury or loss of life (e.g., Dow et al., 2024; Rodriguez, 2025; Swanson et al., 2024; Figure 1). To mitigate these threats, the U.S. Geological Survey (USGS) has developed tools to assist local, state, and federal agencies in rapidly assessing postfire debris-flow risk across California’s diverse geology and geography. This article summarizes that effort and describes ongoing work by the USGS and partners to advance these methods and help California better prepare for future wildfires.

Caliornia↗
USGS2001

Analysis of late Quaternary faulting in San Diego Bay and hazard to the Coronado Bridge

Southern California is transected by numerous pervasive northwest-trending Quaternary fault zones. Together they form the broad transform-fault boundary along which the Pacific and North America crustal plates move irregularly past one another in a right-lateral sense at a rate of about 5 centimeters (cm)/year. The city of San Diego, which lies adjacent to the Pacific Ocean in the southwestern-most corner of California, is cut by one such fault zone -- the Rose Canyon Fault Zone. Oblique movement on faults within the Rose Canyon Fault Zone has, over time, led to the development of San Diego Bay, which separates the metropolitan area of San Diego from Coronado and North Island. The Coronado Bridge spans San Diego Bay and connects the cities of San Diego and Coronado. A principal concern regarding the bridge's earthquake safety involves its proximity, especially of its foundation piers, to potential shallow fault rupture. The objectives of this study were (1) to identify and accurately locate Holocene faults (those younger than about 12,000 years) and (2) to determine the time of the most recent movement on these faults and, therefore, their potential hazard to the Coronado Bridge.

California Geology↗