Seafloor minerals research; supporting discovery of new ore deposits

Author(s): Franklin, James M.
Author Affiliation(s): Primary:
Franklin Geosciences, Ottawa, ON, Canada
Volume Title: Geological Society of America, 2002 annual meeting
Source: Abstracts with Programs - Geological Society of America, 34(6), p.444-445; Geological Society of America, 2002 annual meeting, Denver, CO, Oct. 27-30, 2002. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: Mineralizing processes at seafloor hydrothermal sites are directly observed and measured, reducing uncertainties inherent in interpretation of ancient, deformed and metamorphosed ore-bearing districts. The best example is volcanogenic massive sulfide (VMS) deposits. For these, seawater is down-drawn regionally to cool shallow crustal-level subvolcanic intrusions; these provide heat and drive convective circulation beneath caps which inhibit cross-stratal fluid migration. Trapped fluids reach ∼400C and react with their enclosing strata, imparting a unique mineralogical imprint on the latter and releasing metals to the fluid. Fluids discharge in convective upwelling zones or along caldera- or rift-margin extensional faults. Near-seafloor reactions form distinct alteration pipes. Fluids discharge on or near the seafloor, where rapid cooling induces massive precipitation. Seafloor research contributes as follows: Magma-chamber petrochemical processes are unique to these environments, as shown by the specific occurrence of andesite (Galapagos VMS site). Identification of such petrochemically-unique units helps refine the land-based search in frontier areas. The ODP drill program (Legs 139 & 169; hole 504B) contributed to our knowledge of the reaction zone attributes; Site 857 at Middle Valley provided unequivocal mineralogical and compositional measures that now are applied in ancient sequences. Subseafloor alteration pipes establish sectoral and temporal variations in discharge-zone mineral and chemical attributes(Galapagos, TAG); these provide useable guides to ore in ancient pipes. The volcanological characteristics of caldera (Axial) and rift-related (Endeavour, EPR) synvolcanic faults provide a template for understanding similar preserved sequences. Finally, studies of vent fluids provide knowledge of metal speciation and predict characteristics such as gold contents (Axial, Lau, Havre Trough), sub-seafloor depositional and zone-refining attributes (ODP:TAG & Middle Valley), and far-field vectors from plume fallout. As research extends to new environments (arcs and backarcs) and to greater sub-seafloor depths (proposed TAG and other ODP sites) we will develop new, quantitative exploration guides that will be applied in searching for increasingly scarce mineral resources.
Year of Publication: 2002
Research Program: ODP Ocean Drilling Program
Key Words: 26 Economic Geology, General and Mining Geology; Alteration; Atlantic Ocean; Back-arc basins; Basins; Chemical reactions; Cooling; DSDP Site 504; Discharge; East Pacific Ocean Islands; Extension faults; Faults; Galapagos Islands; Intrusions; Leg 139; Leg 169; Magma chambers; Magmas; Massive deposits; Massive sulfide deposits; Measurement; Metal ores; Mid-Atlantic Ridge; Middle Valley; Mineral exploration; Mineral resources; Mineralization; North Atlantic; Observations; Ocean Drilling Program; Ocean floors; Precipitation; Processes; Quantitative analysis; Research; Sea water; TAG hydrothermal field; Temperature; Upwelling; Variations
Coordinates: N011335 N011338 W0834348 W0834357
N482600 N482730 W1283815 W1284250
N405600 N482800 W1270000 W1284500
Record ID: 2005008990
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