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  • Warren Bates – Geology, alteration and Geophysics an the Manfo Gold Project, Sefwi Belt, Ghana

  


 
 
 
 

    Toronto Geological Discussion Group






 

Warren Bates – Geology, alteration and Geophysics an the Manfo Gold Project, Sefwi Belt, Ghana

  • 09 Oct 2012
  • 4:00 PM - 5:00 PM
  • OBA Conference Centre, Conference Room C&D, Suite 200, 20 Toronto Street in Toronto

Warren Bates, Senior Vice President, Exploration, Pelangio Exploration Inc. will give a presentation on

Geology, alteration and Geophysics an the Manfo Gold Project, Sefwi Belt, Ghana

When: Tuesday October 9, 2012, 4–5 pm followed by networking and refreshments immediately afterward at the Metropolitan Restaurant.

Where: Meeting at the OBA Conference Centre, Conference Room C&D, Suite 200, 20 Toronto Street in Toronto.

Refreshments sponsored by Pelangio Exploration afterward at the Metropolitan Restaurant Bar, 20 Victoria Street, Toronto.

Admission Cost: free for TGDG Members and students. New memberships: New annual TGDG memberships for the 2012-2013 season will be available at the meeting for $25, the same low, low price as last year.

ABSTRACT

The Manfo Project is located in west-central Ghana , approximately 80 km northwest of Kumasi. The project straddles a belt-bounding fault that is the eastern margin of the Sefwi Greenstone Belt. The fault hosts two large deposits 40-50 km to the south, the Bibiani and Chirano gold deposits. On the west side of the belt, 20 km to the northwest , the very large Ahafo gold deposit occupies the belt-bounding margin fault.

Manfo gold mineralization was first drilled in September 2010, and seven mineralized areas have been outlined since, along about 9 km of strike lengthundefinedNfante East, West and Central, Nkansu, Pokukrom East and West, and Sika North.

Mineralized zones are all hosted by quartz-sericite-dolomite-pyrite (qsp alteration) assemblages , with a one-to-one correspondence of gold and pyrite. The habit of qsp alteration zones from outward stockwork (0.2 g/t to 0.5 g/t) to inner massive qsp (0 .5 g/t to 2 g/t) alteration, with gold grades highest in the massive qsp alteration. Very high grades >10 g/t are associated with quartz pyrite veinlets and silicification overprinting massive qsp alteration.

Of the seven mineralized areas discovered to date, the most important is the East Pokukrom Zone, in the east central portion of the property. The zone shows 20-120 m thicknesses of 1 g/t or greater mineralization, along  900 m of a north-northeast-trending, west-dipping fault zone. Post-mineralization brecciation and gouge shows that fault movement continued after gold deposition. A higher grade core of greater than 2.0 g/t mineralization occupies a shallow north-plunging zone of at least 600 m plunge length in the core of the alteration zone.

Outward of the qsp alteration, hematitic alteration is strong in the footwall to the sericite-altered rocks, and very strong in the southwest portion of the mineralization.

Host rocks for qsp alteration are always a biotitic quartzofeldspathic granitoid with accessory magnetite. The biotitic granitoid in outcrop shows  an early NNE west-dipping fabric formed by alignment of biotite. Other precursor rocks include mafic dykes with a basaltic komatiite composition.

The shallow north plunge has yet to be fully explained, and may be due to:
-        an original northwest to southeast compression (thrust);
-        the intersection of a folded preferential compositional layer in the granitoid (magnetic Fe-rich layer?) intersecting the NNE west-dipping fault.

Mafic rocks have very high Mg/Fe ratios and do not host significant gold mineralization. Gra nitoid rocks have reached a peak metamorphic grade of lower amphibolite, and are overprinted by the qsp alteration.

Petrograhic studies show that gold is dominantly fine grained(<50 microns), free and associated with the core of hypidiomorphic pyrite grains. The outward portions of the hypidiomorphic pyrite are zoned in layers, alternating in arsenian pyrite to low arsenic pyrite. Another mineral directly related with the gold mineralization is hydrothermal barite.

Gold mineralization is directly related to hydrothermal pyrite formation; it is also related to the very low magnetic susceptibility of the host rock.

Of 37,300 meters drilled to date, each meter has been measured for magnetic susceptibility; gold is associated with very low magnetic susceptibility associated with pyrite-rich sericite-altered granitoid.

The terrane is strongly weathered to saprolite to at least 35-50 meters, outcrop is rare, and the existing outcrop often denies recognition of what the parent identity is.  Airborne magnetic surveys and IP (gradient ) and pole-dipole IP surveys have been carried out, and results of the IP, resistivity and magnetic surveys will be shown with respect to mineralized material.

The best tool to date for delineating structure is the combination of magnetic data and sericite alteration mapped in drilling. A magnetic susceptibility model is being constructed in Leapfrog, and inversions of magnetic susceptibility on combined airborne and drilling datasets will be completed in the next quarter.

Drilling magnetic shoulders in the absence of strong geochemical indicators has shown the mineralization at Nkansu. Mineralization style, gold grain size distribution and host rocks are similar to Ahafo. Metallurgical behavior, with recoveries in sulfide of 85-90%, are very similar to Ahafo, host rocks similar to the Ahafo Subika deposit.

Maiden resource will be completed on Pokukrom East , West and Nfante West in Q1 2013. Additional surface programs are being performed along trend, and additional drilling is to be carried out at all seven zones in 2013.

BIO

Warren completed a B.Sc (Hons ) geology degree at the University of Manitoba in 1985, summers were spent working for BP/Selco, and on graduation, he went to work for Granges Exploration Inc. Warren worked as a project geologist until 1992, in the Flin Flon – Snow Lake belt, and initiated Granges’ move eastward to Ontario in 1986. After six years in Timmins, Ontario, Warren became Canadian Exploration Manager. Canadian exploration included VMS, Kambalda nickel, orogenic gold, diamond breccia pipes and porphyry Cu-Au, and  Eskay-type VMS gold in the greenstones and BC Cordillera. In 1996, Warren was transferred to Denver, Colorado, and assumed responsibilities working in Latin America, including work in Ecuador, Chile, Bolivia, Peru and Venezuela. Work was concentrated on upper level gold and porphyry exploration, with a dash of orogenic gold exploration in Venezuela. From 1999 to 2005 Warren worked as a VP exploration for Vista Gold, Granges’ successor. Responsibilities included project acquisition, reserve and resource definition, reconciliation of block models to actual production, and especially the relation of geology to modeling. Warren worked as VP Exploration for St. Andrew Goldfields from 2006 to 2007, and has been VP Exploration for Pelangio Exploration since September 2007, working mostly in Ghana, a return to pure exploration in orogenic gold.



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