2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 277-10
Presentation Time: 11:00 AM


LAWRENCE, Andrew C., SUTTERFIELD, David R., ARNOFF, Michael J., FLETCHER, Andrew W., MATHESON, Ephram C., KERSWELL, Buchanan, NATTER, Daniel H., FELLOWS, Steven A. and EMERMAN, Steven H., Department of Earth Science, Utah Valley University, 800 West University Parkway, Orem, UT 84058

Gossans are intensely oxidized and weathered rock outcrops commonly associated with ore deposits. Gossans are generally thought to form when sulfide minerals become oxidized, altered, and leached, and are then replaced by silica and iron oxide/hydroxide minerals that develop cellular structures called boxworks. These boxworks often retain the shape of the original sulfide minerals. However, not all gossans are associated with ore deposits. Pyrite and other non-ore minerals can become weathered and exhibit similar surficial expressions. Our overall aim is to develop a methodology that allows for rapid and efficient classification of gossans, linked to their likely original sulfide mineral assemblage, prior to costly drilling operations and time-intensive geophysical surveys. To this end, we are carrying out analyses of 100 gossan samples to be collected from three ore deposit types (porphyry copper, epithermal polymetallic vein, and skarn deposits) in order to quantify their physical and chemical signatures. We hypothesize that immobile trace elements and physical features of the original sulfides are encoded within the gossan. These relicts are unique to the original ore deposit type or responsible sulfide assemblage. A Bruker Tracer III-SD Handheld XRF Analyzer is being used to analyze gossan samples that are collected, powdered, and homogenized from known ore deposits found within Utah. This method facilitates rapid identification of unique trace elemental signatures particular to known ore deposit types. These data will be used to form a unique “fingerprint” of the gossans associated with each ore deposit type. Additionally, we are quantifying the unique physical properties of the gossan such as the structure of the boxworks using geospatial (GIS) software. All results will be compared with samples collected from non-mineralized gossans to determine the difference in chemical and physical parameters between ore deposits, and gossans hosting no known ore minerals. In the future this study will be expanded to include gossan analyses from a wide array of ore deposit types and will be used as a tool for targeting various undiscovered ore deposits.
  • Lawrence GSA Gossan Presentation 2014_SF_Update_smaller.pptx (42.9 MB)