Graduation Year

2025

Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Science

Department

Environmental Analysis

Second Department

Geology

Reader 1

Jade-Star Lackey

Reader 2

Colin Robins

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Terms of Use for work posted in Scholarship@Claremont.

Abstract

This thesis investigates the geologic history of malachite and azurite samples in the mineral collection of the Pomona College Geology Department, utilizing stable carbon and oxygen isotopes. Samples in this study are concentrated in the copper-rich Southwestern United States, particularly around the historically significant Bisbee-Warren mining district in Arizona. Malachite(Cu₂CO₃(OH)₂) and azurite (Cu₃(CO₃)₂(OH)₂) are copper carbonate minerals that form as pseudomorphs under various environmental conditions. These minerals crystallize in oxidized zones of copper ore deposits and display diverse crystal habits reflective of unique formation conditions with influences from formation fluid, depth of mineralization, carbonate activity, and atmospheric CO₂. Given the extensively undocumented nature of the collection, a major goal of the thesis was to test whether stable isotope signatures could serve as a geochemical fingerprint for provenance. Analysis of stable oxygen and carbon isotope ratios of carbon dioxide liberated from selected malachite and azurites show a broad trend of increasing oxygen-18 values correlated with decreasing carbon-13 values, with most malachites reflecting near-surface, meteoric water-influenced environments. Isotopic analysis of azurite-malachite pseudomorphs exhibited additional trending, with azurite consistently higher in oxygen-18 and carbon-13 than its malachite counterparts. These isotopic offsets reinforce the understanding of environmental transitions during pseudomorphic transformation. The narrow clustering of isotopic results provides strong evidence to support the hypothesis that the majority of the samples studied originated from the Southwestern U.S. This thesis integrates mineralogical observations with stable isotope geochemistry to study the environmental conditions under copper carbonate formation to help trace their geographic origin.

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