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Overview

solar panels
Alamosa Solar Generating Project was the largest high concentrating solar photovoltaic power station in the world when it was completed in 2012. It is located on 225 acres in the San Luis Valley near Alamosa, CO. Photograph by Dennis Schroeder, NREL.

Why are we doing this research?

Tellurium, which is used in metal alloys, semiconductors, and in the rapidly growing solar energy field, is recovered as a primary resource from only two locations in the world: the adjacent Dashigou and Majiagou deposits in southwestern China and the Kankberg deposit in Sweden. Currently, about 85% of global production of tellurium comes as a byproduct of copper mining through a process called electrolytic refining.

However, there is currently a shift in the mode of production of copper (to increase recovery of copper) from electrolytic refining to solvent extraction-electrowinning (SX-EW) and recycling. Recycling and solvent extraction-electrowinning do not produce tellurium as a byproduct, and therefore, the future supply of tellurium will be greatly reduced. Meanwhile, more tellurium will be required as more solar fields are built. In light of this, it is imperative that we understand the enrichment processes of potential alternative sources of tellurium, such as epithermal gold deposits. From a national security viewpoint, it is a great benefit that there are known domestic occurrences of these deposits.

Tellurium in Colorado and New Mexico Deposits

It is commonly assumed that most epithermal gold deposits associated with alkaline igneous rocks (deficient in silica with respect to alkalis) are enriched in tellurium, and within Colorado and New Mexico, many deposits are indeed tellurium-rich. However, many known alkalic-related deposits contain low tellurium concentrations. Alternatively, significant tellurium concentrations are associated with some calc-alkaline epithermal gold deposits. Cripple Creek and deposits in the Jamestown district in Boulder County are alkaline-related gold deposits in which gold resides primarily within gold-tellurium minerals. Whole rock ore samples from Cripple Creek and Boulder County contain tens of parts per million to over 0.1% tellurium. However, very few of the alkaline-related epithermal deposits in New Mexico contain significant concentrations of tellurium. The Lone Pine calc-alkaline epithermal gold deposit, which contains gold-tellurium minerals and native tellurium, has been the only producer of tellurium in New Mexico.

What research is USGS going to do?

The project has three primary areas of study:

  • Geology, geochemistry, mineralogy, and geochronology
  • Processes of enrichment
  • Exploration methods

The contrast between tellurium-rich and tellurium-poor alkaline-related epithermal gold deposits may be attributed to differences in underlying basement compositions (and indirectly, magma composition), although this is not well documented. In general, the causes of enrichment remain unclear. Thermodynamic modeling suggests that tellurium is largely carried in the vapor phase as gaseous tellurium species in magmatic fluids. This project is a field and laboratory based investigation on tellurium resources in epithermal gold deposits that is designed to answer these questions:

  • Is parental magma composition a controlling factor?
  • What are the processes of tellurium transport in magmatic-hydrothermal fluids?
  • Are there specific zones within a district where tellurium is found?
  • Can we fingerprint tellurium-bearing systems from those that are tellurium-poor using geophysical parameters as proxies for basement or magma composition (e.g., physical or magnetic properties)?

What are anticipated outcomes?

The project aims to improve our understanding of the causes of tellurium enrichment in epithermal precious metal deposits, and strengthen our ability to assess the Nation's tellurium deposits.

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Project Activities

field work in Jicarilla Mountains
USGS geologists and collaborator from New Mexico Bureau of Geology and Mineral Resources examine rocks in the Jicarilla Mountains, New Mexico. Photograph by Karen Duttweiler Kelley, USGS.

The initial focus of our research will be on the tellurium-rich deposits at Cripple Creek, Colorado and one tellurium-poor system in New Mexico (Jicarilla Mountains). Previous research at Cripple Creek has provided a foundation of abundant existing data. The geochronology of intrusive/extrusive phases that preceded and coincided with mineralization at Cripple Creek has been well established, and the petrologic evolution and origin of the magmas was determined using radiogenic isotope compositions and geochemistry.

Geology, Geochemistry, Mineralogy, and Geochronology

Contact: Karen Duttweiler Kelley, kdkelley@usgs.gov

We will compile all existing geochemical data for the Colorado-New Mexico region. We will analyze unmineralized basement and magmatic rocks from Cripple Creek, Colorado, and unmineralized and mineralized samples from the Jicarilla Mountains, New Mexico for tellurium and other elements. In addition to geochemical analyses, select samples will be measured and analyzed for age-determinations. We will analyze mineral assemblages to determine paragenetic relationships and mineral chemistry.

Processes of Enrichment

Contact: Erin Marsh, emarsh@usgs.gov

We will use integrated analytical techniques to determine the chemical parameters that allow for tellurium enrichment, transport, and deposition: scanning electron microscope, electron microprobe, cathode luminescence, QEMSCAN, microthermometry, Raman, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). In the case of Cripple Creek, we will analyze melt inclusions from different phases of igneous rocks and if possible, link these to the evolution of the magmatic system because the sequence of intrusions and extrusive activity has been previously established. We will analyze fluid inclusions from ore samples to determine the conditions (volatile contents and metal concentrations) leading up to and coinciding with mineralization.

fluorite telluride mineral sample
High-grade mineralized rock from Cripple Creek containing purple fluorite and telluride minerals (in vugs). Width of photo is about 10 cm. Photograph by USGS.

Exploration Methods

Contact: Eric Anderson, ericanderson@usgs.gov

We will use publically available geophysical data sets to determine the geophysical expression of ore-related igneous rocks and use this information to assess additional resources under cover. We will link observed geophysical anomalies to physical property measurements and geochemical analyses. Filtering techniques to highlight components of magnetic and gravity data will be related to mapped geology. We will investigate whether melt inclusion elemental concentrations reflect the basement rock geochemistry and what additional information can be determined from the geophysics of the underlying basement.

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Products

Abstracts

Anderson, E.D., Kelley, K.D., Marsh, E.E., and Weisberg, W.R., 2016, The use of potential field data in characterizing basement rocks and igneous suites near the tellurium-rich Cripple Creek alkalic epithermal deposit, Colorado: Geological Society of America Abstracts with Programs, Vol. 48, No. 7, doi:10.1130/abs/2016AM-286629.

Kelley, K.D., and McLemore, V.T., 2016, Critical elements in alkaline igneous rock-related epithermal gold deposits: Geological Society of America Abstracts with Programs, Vol. 48, No. 7, doi:10.1130/abs/2016AM-280787.

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Project Contacts

Erin Marsh
Phone: 303-236-2473
Email: emarsh@usgs.gov
Central Mineral and Environmental Resources Science Center

Karen Duttweiler Kelley
Phone: 303-236-2467
Email: kdkelley@usgs.gov
Central Mineral and Environmental Resources Science Center

Mineral Resources Program Science Priority

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