The Laramide Caborca orogenic gold belt of northwestern Sonora, Mexico; white mica 40Ar/39Ar geochronology from gold-rich quartz veins

Open-File Report 2016-1008
By: , and 

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Introduction

This report contains reduced 40Ar/39Ar geochronological data from 63 hydrothermal white mica samples separated from orogenic gold-rich quartz veins in the Laramide Caborca orogenic gold belt (COGB) of northwestern Sonora, Mexico. The main objective of this report is to present the sample locations, 40Ar/39Ar experimental methodology, and 40Ar/39Ar isotopic data. We include age spectra and inverse-isotope correlation diagrams for all white mica samples. The age spectra are separated into three groups based on the type of age used for geologic interpretation, including plateau ages (group 1), isochron ages (group 2), and average or single-step heating ages (group 3). The resulting age spectra are used to help establish the age of mineralization for the COGB.

The COGB is approximately 600 kilometers long and 60 to 80 km wide, trends northwest, and extends from west-central Sonora to southern Arizona and California. The COGB contains mineralized gold-rich quartz veins that contain free gold associated with white mica (sericite), carbonate minerals (calcite and ankerite), and sulfides such as pyrite and galena. Limited geochronologic studies exist for parts of the COGB, and previous work was concentrated in mining districts. These previous studies recorded mineralization ages of approximately 70 to 40 Ma. Therefore, some workers proposed that the orogenic gold mineralization in the region occurred during a single pulse that was associated with the Laramide Orogeny that took place during the Cretaceous to early Eocene in the western margin of North America. However, the geochronologic dataset was quite limited, making any regional interpretations tenuous. Accordingly, one of the objectives of this geochronology study was to get a better representative sampling of the COGB in order to obtain a more complete record of the mineralization history. The 63 samples presented in this work are broadly distributed throughout the area of the COGB and allow us to better test the hypothesis that mineralization occurred in a single pulse.

Suggested Citation

Izaguirre, Aldo, Kunk, M.J., Iriondo, Alexander, McAleer, Ryan, Caballero-Martínez, J.A, and Espinosa Arámburu, Enrique, 2016, The Laramide Caborca orogenic gold belt of northwestern Sonora, Mexico; white mica 40Ar/39Ar geochronology from gold-rich quartz veins: U.S. Geological Survey Open-File Report 2016–1008, 30 p., http://dx.doi.org/10.3133/ofr20161008.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Introduction
  • Methods
  • Results of 40Ar/39Ar Data
  • Conclusions
  • Acknowledgments
  • References Cited

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title The Laramide Caborca orogenic gold belt of northwestern Sonora, Mexico; white mica 40Ar/39Ar geochronology from gold-rich quartz veins
Series title Open-File Report
Series number 2016-1008
DOI 10.3133/ofr20161008
Year Published 2016
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Eastern Geology and Paleoclimate Science Center
Description Report: iv, 30 p.; 4 Tables
Country Mexico, United States
State Arizona, California, Sonora
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
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