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MULTIDISCIPLINARY APPROACH TO POSSIBLE METALLOGENIC MODELS AND TYPES OF PRIMARY GOLD CONCENTRATION IN THE GRETACEOUS ARC TERRANES OF DOMINICAN REPUBLIC

Objective

The objective of this project is to further assess the gold potential of the poorly known Michess area (90 km superscript 2) in the Dominican Republic, by comparison with the better known Pueble Viejo active gold mine in the Central Cordillera.
The gold potential of the poorly known Miches area (90 km{2}) in the Dominican Republic was assessed by comparison with the better known Pueblo Viejo active gold mine in the Central Cordillera. In addition, the amenability of selected ore samples from this region to downstream processing was investigated using nontoxic or less toxic leaching agents.

Fieldwork revealed, within and around the Miches area, unexpected targets for primary gold although not comparable with the Pueblo Viejo deposit.

Research was designed to investigate the use of thiocyanate based leaching systems for the extraction of gold from ore samples.
The main variables of the thiocyanate leaching system were thiocyanate concentration, iron(III) concentration, iodine concentration and pH.
The results were very promising, with both rates and overall gold recoveries being identical to, or greater than, those observed in the respective cyanide leach test.
The level of oxidant addition was a major factor in determining the final gold recovery. This highlighted the need for effective oxidative potential (Eh) control, in order to maintain the potential above 600 mV, in any plant operating withthiocyanate.

Preliminary carbon adsorption tests have been carried out using synthetic thiocyanate liquors. The results show high gold adsorption rates. However, a loss of solution colour over the period of the adsorption test suggested that either iron(3+) ions are being coadsorbed onto the activated carbon or that the iron(3+) is being reduced at the carbon surface leading to excessive consumption of reagents making this route economically nonviable.

The subsequent stripping of the gold from the loaded carbon has also been studied. Conventional carbon stripping was carried out at elevated temperatures using a strong caustic cyanide/ethanol solution. Initial tests substituting iron(3+)/thiocyanate for the caustic cyanide were found to be unsuccessful (again colour loss from the solution suggested the same mechanism as in adsorption stage was occurring). However it was found that if the loaded carbon was first subjected to an acid preleach, the gold could then be stripped from the carbon via the conventional caustic cyanide/ethanol route.
The work programme will consist of the following 4 phases, each corresponding to a specific methodology and representing the successive milestones of the project. Firstly, definition and evaluation of the primary gold sources via assessment of metallogenic models involving: .SP 0 a field survey comparison between El Saybo, los Ranchos and El Oro units (possible source-rocks), lithostratigraphy, and sample collection for petrography;
a field survey evaluation of the importance and extension of El Saybo lithologies overthrusting El Oro sequences (sample collection for petrography);
lineament analysis (field work) and comparison with remote sensing data and field controls;
hydrothermal alteration pattern (deducted from remote sensing data) and related mineralization analysis, field controls and comparisons with Pueblo Viejo.

Secondly, field studies involving:
lithogeochemical profiles in the Miches area (major and minor elements) and obtention of reference profiles on Pueblo Viejo;
a check for gold bearing orebodies, predictable on the basis of the correct plate tectonic assessment of the Miches and El Saybo area;
and geophysical data acquisition and interpretation on the alteration zones.

Thirdly, laboratory work involving:
petrographical, sedimentological, paleontological and mineralogical investigations, analysis and interpretation;
chemical, microchemical (electron microprobe) and stable isotopes (oxygen, carbon, hydrogen) analyses;
and analyses of hydrothermal alteration patterns by mineralogical, fluid inclusion and mineral equilibria studies.

Lastly, mineral processing involving:
mineralogical analysis on gold state in the ores (ion microprobe analyses and Mossbauer spectroscopy);
application of new leaching technologies, using thiocyanate and thiourea solutions and experimental investigations using aqueous thiosulphide solutions;
joint and cooperative elaboration and data computing, discussion and conclusion, preparation and editing of the final report.

Coordinator

Euromin Srl
Address
Via Donota 1
34121 Trieste
Italy

Participants (3)

Imperial College of Science, Technology and Medicine
United Kingdom
Address
Prince Consort Road
SW7 2BP London
NATIONAL RESEARCH COUNCIL OF ITALY
Italy
Address
Via Bolognola 7
00138 Roma
Università degli Studi di Padova
Italy
Address
Corso Giuseppe Garibaldi 37
35137 Padova