Beyond the Obvious Limits of Ore Deposits: The Use of Mineralogical, Geochemical, and Biological Features for the Remote Detection of Mineralization

• DOI: 10.2113/gsecongeo.101.4.729
• Publication Date: 2006-10-31T11:28:03Z
• Authors: D. L. Kelley; K. D. Kelley; W. B. Coker; B. Caughlin; M. E. Doherty
• Keywords: Tourmaline

Far field features of ore deposits include mineralogical, geochemical, or biological attributes that can be recognized beyond the obvious limits deposits. They primary, if formed in association with mineralization alteration processes, secondary, from interaction hydrosphere and biosphere. This paper examines a variety far different deposit types considers novel applications to exploration discovery.

Primary mineral rock chemistry, isotopic element halos, fluid pathways thermal anomalies host-rock sequences. Examples use apatite chemistry distinguish intrusive rocks permissive for iron oxide copper gold (IOCG) porphyry deposits; resistate (e.g., rutile, tourmaline) volcanogenic massive sulfide (VMS), orogenic gold, pyrite vector toward sedimentary exhalative (sedex) Distinctive whole-rock geochemical signatures also as feature For example, unique Sr/Y ratios samples, used barren versus fertile magmas Cu mineralization, result differentiation oxidized hydrous melts. Anomalous concentrations halogen elements (Cl, Br, I) have been found distances up 200 m away some mineralized centers. Variations composition between ore-bearing intrusions and/or systematic vertical lateral zonation sulfur, carbon, oxygen isotope values documented types. Owing aureole extends area deposits, detection paleothermal effects through methods such conodont indices, vitrinite bitumen reflectance, illite crystallinity, zircon thermochronology studies valuable, particularly low-temperature history.

A number newly investigated secondary development reduced columns by electrochemical processes transported overburden, dispersion related expulsion groundwater tectonic seismic compression, vapor above processes. Redox gradients underlying overlying environments associated bodies, which mass transfer dispersion. Recent characterized pH, oxidation-reduction potential (ORP), self (SP) overburden sulfide-hosted VMS Lateral migration metals is well understood normal flow, but responsible its dissolved components only recently. One process, termed cyclical dilatancy pumping, expels during after earthquake events, cause redistribution around environments. Soil gases are interest owing their high degree mobility vadose zone overburden. Numerous soil gas species (CO2, O2, Hg, Rn, He, sulfur compounds, light hydrocarbons) measured interpreted diagnostic buried evidence suggests possible link metal enrichment soil. Geochemical plant material soils successive growth-death cycles established, important role microorganisms now increasingly evident. Microorganisms significantly enhance kinetics oxidation influence distribution The presence metal-resistant bacteria enhanced sulfate-reducing exotic over these organisms attracted this environment and, therefore, may indicators under cover.

Many few case studies. Additional research required determine scale features, controls on formation, consistency they measured. Incorporation detecting into field-based programs increase probability success, especially covered terrains.