Lithophile and Chalcophile Elements in Sphalerite from the Anarraaq Sediment-Hosted Zn-Pb-Ag Deposit, Red Dog District, Alaska

• Author / Creator

  Smith, Devon L

• The age of many sedimentary hosted base metal deposits has been a topic of debate for several decades, due to a lack of minerals ideal for geochronological age in these systems. One technique is focused on dating the ore minerals (sphalerite) directly with the Rb-Sr method. The main issue with the application of this technique is that the location of the Rb and Sr has never been definitively identified in sphalerite. It has been proposed that the Rb and Sr could be lattice bound, perhaps involved in a coupled substitution, however, this is unlikely due to the much larger size of these ions, relative to Zn. Furthermore it has been suggested that the Rb and Sr could potentially reside in mineral inclusions within the sphalerite which would compromise the accuracy of the method. This study uses sphalerite from the Anarraaq deposit, Alaska, to address whether the Rb and Sr are hosted in the sphalerite or in mineral inclusions which may not be co-genetic with sphalerite precipitation. The Red Dog district of Alaska is a world class sediment-hosted Zn-Pb district. The Anarraaq deposit lies approximately 10 km NW of the main Red Dog deposits and hosts an additional inferred resource of 19.4 Mt at 14.4% Zn and 4.2% Pb. Zinc-lead mineralization in the Red Dog district is hosted by organic-rich mudstones which were deposited in a passive margin setting in the mid-late Mississippian. The Anarraaq sphalerite has been divided into 6 distinct generations based on textural variation and cross-cutting relationships. Variability in color also exists within each of the 6 sphalerite stages and textures include spherical, fibrous, bladed, and oscillatory zoned colloform banding. Following characterization of the textural variability and reconnaissance electron microprobe analyses (EMPA), element mapping of Rb, Sr, Al, Si, Fe, Cu, Ge, As, Ag, Cd, Sb, Hg, Tl, and Pb was conducted using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). The laser was modified with an aerosol rapid induction system (ARIS). This advanced mapping technique involved using a series of high speed laser ablated line scans combined with unconventional laser ablation operating conditions such as low laser fluence and high laser repetition rate. This application of LA-ICPMS mapping provides new information about the complexities of trace element distributions in Anarraaq sphalerite which include Fe controlled oscillatory zoning, oscillatory zoning independent of Fe content, sector zoning, and mineral inclusions. Strontium is mostly hosted in carbonate mineral inclusions within the sphalerite. This study does not show evidence that supports a coupled substitution involving Rb in the sphalerite lattice. Rubidium is hosted in silicate mineral inclusions which cannot be determined to be syngenetic with the sphalerite and this would prevent any accurate Rb-Sr dating of this deposit.

• Subjects / Keywords

  • Sphalerite
  • Red Dog, Alaska

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3TM72F4R

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.