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.
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.
The project has three primary areas of study:
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:
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.
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.
Contact: Karen Duttweiler Kelley, firstname.lastname@example.org
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.
Contact: Erin Marsh, email@example.com
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.
Contact: Eric Anderson, firstname.lastname@example.org
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.
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.
Central Mineral and Environmental Resources Science Center
Karen Duttweiler Kelley
Central Mineral and Environmental Resources Science Center