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TECTONIC CONTROLS ON CHROME ORE LOCALIZATION IN OPHIOLITES, GREECE.

Objective

THE PRACTICAL APPLICATIONS RESULTING FROM THE RESEARCH WILL BENEFIT MINERAL EXPLORATION PROGRAMMES IN OPHIOLITES TERRANE IN THE FOLLOWING WAYS:

- CONSIDERATION OF BRITTLE TECTONIC STRUCTURAL TRAPS OF MASSIVE CHROMITE ORES MAY LEAD TO PREDICTION OF "BLIND" CHROME DEPOSITS IN THE OTHRIS OPHIOLITES.

- RECOGNITION OF DIAPIRIC ZONES IN THE PINDOS UPPER MANTLE SUITE COULD REDUCE EXPLORATION AREAS FROM HUNDREDS TO TENS OF SQUARE KILOMETERS.

- CERTAIN GENETIC TYPES OF OPHIOLITES MAY PROVE ORE-BARREN COMPARED TO OTHERS. IN THIS WAY, ENTIRE COMPLEXES CAN BE CLASSIFIED AS HIGH- OR LOW- EXPLORATION PRIORITY.

- DEFINITION OF THE MAGMATIC ENVIRONMENT OF KNOWN OCCURENCES AND CORRELATION WITH HOST ROCKS OF UNKNOWN POTENTIAL CAN RESULT IN A GENERAL GUIDE FOR MINERAL EXPLORATION IN BASIC-ULTRABASIC ROCKS.
Methodologies have been developed and applied to the location of chromite ores within the Vourinos, Pindos and Othris ophiolitic terrains of Greece.
Basic topics of research were:
detailed structural studies over the Vourinos ophiolite complex, aiming at understanding the role of mantle and emplacement tectonics in the present form and distribution of chromite (a drilling programme has subsequently located significant blind ore deposits);
small scale structural studies over large areas of Pindos and Othris ophiolites, accompanied by aeromagnetic surveys, in order to locate critical areas for chromite exploration;
limited petrographic and geochemical studies as a supplement to structural studies.

The primary goal of the project was to further the understanding of the structural setting of ophiolitic chrome ores in order to aid subsurface exploration. The 3 largest ophiolites of Greece (Vourinos, Othris and Pindos) contain over 1600 km{2} of peridotites potentially hosting chromite orebodies.
It is hypothesized that structural setting, in addition to tectonogenetic affinity, is the controlling factor in preservation and position of economic chromite deposits.
The most promising target for future exploration is the uppermost 100 to 200 m of peridotite underlying known ore districts or promising chromite showings. Ophiolitic chrome orebodies are highly deformed, irregular in shape, and comprise small exploration targets.
Recent research demonstrated a close correspondence between local structure and the position of orebodies. The present project developed and applied this correspondence to a viable chrome ore exploration strategy in the following ways:
screening of vast areas of ore destructive tectonic domains;
identification of specific types of tectonic ore traps;
tectonic interpretation of ductile and brittle fabric measurements.

It was found that chromite deposits in ophiolitic hosts were confined to structural traps generated during ductile obduction processes and accentuated by brittle emplacement strain.
Exploration criteria for chrome ore bodies in ophiolites resulting from and confirmed by the research are as follows:
location of ophiolitic sections originally in close proximity to the petrologic Moho or spreading ridge;
analysis of obduction strain;
determination of position within the obducting mantle slab;
evaluation of potential ore traps;
indication of elongation directions (spinel fabrics are highly affected by ductile overprint in such a way that spinel lineations and chrome ore fold axes indicate the elongation directions of potential orebodies).
THE PROJECT WILL BE DIVIDED INTO SEMI-INDEPENDENT RESEARCH TOPICS WHICH ARE:

- DELINEATION OF MAIN TECTONICS SHEETS OF PERIDOTITE IN THE OTHRIS AND PINDOS OPHIOLITES BY MAPPING, REMOTE SENSING AND INTERPRETATION OF AEROMAGNETIC DATA.

- INVESTIGATION AND MAPPING OF INTERNAL-THRUST TECTONICS OF THE MAJOR PERIDOTITE SHEETS, AND CORRESPONDENCE TO ORE LOCALITIES BY ON-SITE INSPECTION.

- A DETAILED STUDY OF HIGH-TEMPERATURE PERIODOTITE FABRICS IN THE PINDUS THRUST SHEEST, RELATING TO UPPER MANTLE SITES OF ORE DEPOSITION.

- CONTINUATION OF THE VOURINOS RESEARCH WITH PARTICULAR EMPHASIS ON THE RECOGNITION OF ORE-POSITIVE DEFORMATION ZONES BY TECTONIC AND RE-EQUILIBRATION CRITERIA.

THE INTEGRATION OF THESE STUDIES WILL RESULT IN FORMULATION OF A NEW CHROMITE EXPLORATION METHODOLOGY FOR EACH OF THE THREE OPHIOLITIC SYSTEMS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Institute of Geology and Mineral Exploration
Address
70,Messogeion Street
11527 Athens
Greece

Participants (2)

UNIVERSITY OF SOUTHAMPTON
United Kingdom
Address
Southampton Ocenagraphic Centre, European Way
SO14 3ZH Southampton
Université de Montpellier
France
Address

Montpellier