Guitermanite (Jordanite, etc.) with Zunyite
specimen number:
2262099
location:
Zuni Mine, San Juan Co., Colorado, USA
description: The Zuni Mine, located on Anvil Mountain near Silverton in San Juan County, Colorado, is a significant hydrothermal chimney deposit within the Silverton Caldera complex. Geologically, the site consists of a highly altered, pipe-like ore body hosted in Tertiary volcanic rocks, characterized by intense advanced argillic alteration that produced a unique suite of rare minerals including zunyite and various lead-arsenic sulfides. Historically, mining and quarrying activities at the Zuni Mine began in the early 1880s following the discovery of high-grade silver and lead ores, with the most active period of production occurring between 1883 and the early 1890s. While small-scale exploration and specimen recovery efforts occurred intermittently throughout the 20th century, the mine is primarily remembered today as the type locality for several rare species and remains a focal point for mineralogical research into the geochemistry of San Juan Mountain ore systems through 2026. Guitermanite was originally described as a distinct lead arsenic sulfide mineral from the Zuni Mine, but modern analytical techniques suggest it is likely a fine-grained, bluish-gray massive phase of jordanite or a complex mixture of related species. Geologically, it occurs within the dense, metallic ores of the Zuni chimney, often appearing as a metallic, fine-grained material that lacks well-defined crystal faces and is frequently intergrown with other rare sulfides. While once considered a unique species, mineralogical studies have indicated that many specimens labeled as guitermanite actually consist of jordanite, zunyite, and potentially other yet-to-be-identified mineral phases or sub-microscopic inclusions. The status of guitermanite as a valid mineral species remains a subject of historical interest and ongoing scientific debate, as researchers continue to use advanced diffraction and spectroscopic methods through 2026 to unravel the true identity of these complex lead-arsenic mineral assemblages from the Silverton district. Frederick Leslie Ransome was a preeminent American economic geologist who played a fundamental role in the systematic study of North American ore deposits during the early 20th century. After earning his PhD from the University of California, Berkeley, in 1896, Ransome joined the United States Geological Survey (USGS), where he authored several landmark monographs that defined the geological understanding of major mining districts. His meticulous field investigations and descriptive work at iconic localities, such as Cripple Creek, Colorado, and the Coeur d'Alene district in Idaho, became the gold standard for correlating structural geology with mineral paragenesis. Ransome's career spanned a transitional era in the earth sciences, moving from purely descriptive mineralogy to the rigorous application of physicochemical principles to explain the origin of ore-bearing fluids. Beyond his work with the USGS, he served as a professor at both the University of Arizona and the California Institute of Technology, influencing generations of geologists until his death in 1935. Today, his detailed maps and professional papers remain essential reference materials for researchers studying the tectonic evolution and mineral wealth of the American West.
Rich masses of what used to be called guitermanite, this now found to be a mixture mostly of the mineral jordanite in several other species, with minor zunyite along one edge. Interesting historical specimen, this was collected by the famous geologist F.L. Ransome in 1899., The oldest is actually in four sections.
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