By Nandkumar M Kamat
The Government of Goa after taking cognizance of the sensitive information revealed in this article based on my research should promptly take over all the iron ore reject dumps in north Goa and set up on site screening plants in the public sector for mechanical separation of the precious gold fraction.
It would make Goa the richest state in the world. The non polluting technique for separation of gold fraction would be freely transferred to the state government in public interest. Auriferous ore rejects brought and piled up in dumps as overburden from banded ferruginous quartzites (BHQ) mines in north Goa can yield up to 5 - 50 kg of gold per MT (metric tone).
Gold is ridiculously easy to detect because it is a noble metal not oxidized in nature. This raises the question - how did such a resource get undervalued all these years? The Government and industry has missed what a high school student can demonstrate in less than half an hour without any costs.
The Geological Survey of India (GSI), IMB (Indian bureau of Mines) may have known the fact but must have opted for diplomatic silence. Despite endowed with chemically the most diverse and creative Archean rocks in western Dharwar craton (WDC), Goa lacks an intensive knowledge based mining policy which makes it mandatory to reveal the detail geochemical composition (esp heavy metals and rare earths if any) of the mined material in ppm or ppb concentration. The policy should not have allowed export of ore without proper valuation of economically exploitable non ferrous metals by experts.
So far the government is concerned with ores containing only three metals – iron (hematite, Magnetite, Goethite, Limonite), manganese (Pyrolucite and Psilomelane) and aluminium (bauxite). There is zero interest in other economically valuable metal content despite the boom in the non ferrous metal commodity market. The estimated iron ore reject in Goa piled up in dead and active dumps would be about one billion metric tones.
Since 2002, some of these dumps have been excavated legally or illegally and the low grade iron ore has been exported. The position of such dumps can be ascertained by using the Historical Imagery Tool of Google Earth.
China and Japan has been quietly extracting gold from the imported low grade iron ore of Goa. There is no end user agreement between the Chinese importers and Goa’s iron ore exporters about extraction of gold or other useful non ferrous metals. Our latest findings indicate that the mining reject from banded ferruginous quartzites (BHQ) belt of north Goa is shockingly rich in gold.
The gold is in particulate and unique nanoparticulate form with typical surface plasmonic resonance features comprising a sizeable microbiogenic fraction which I found surprisingly identical to what I had reported in January 2011 from lensoid tilloid sample from deep metabiosphere under Sanvordem formation. The gold particles including the microbiogenic ones are less than 150 microns in size and can be detected even by high school students using a simple procedure.
Goa’s BHQs are included among world’s most ancient, pre Cambrian (2.6-3.2 billion years old) iron deposits which are classified under BIF- Banded Iron Formation. Henceforth a holistic, knowledge based policy would be required to utilise BIF.
According to Dr Ashok Dessai (2011) "banded ferruginous quartzites (BHQ) occur as intercalations within the phyllites. The BHQs serve as the protores for the iron ore deposits that are extensively developed in this formation. The BHQs are thinly laminated and consist of alternate laminae of hematite / magnetite and chert. Magnetite is invariably martitised. The banded iron formation (BIF) consists of two subfacies - the haematite sub-facies and the magnetite sub-facies, both of which show interdigitated relationship. The hematite sub-facies predominates in the north-western and central part (from Advalpal to Dharbadora) of the State whereas the magnetite sub-facies is largely confined to the central and the southeastern part (Costi to Barazana-Villiena). Calcareous (carbonate facies of BIF) and carbonaceous (sulphide facies) intercalations are common. The BIF of the Bicholim Formation is suggestive of chemogenic precipitation under quieter conditions in relatively deeper parts in closed environments. Lateral variations with the haematite sub-facies in the north progressively grading into the magnetite sub-facies in the central and south Goa represents platformal-type of deposition. Minor limestones and silica suggest presence of algal activity."
I found the last sentence very useful to justify the presence of microbiogenic or bacterioform gold which we have detected. How can gold be found in Goa’s banded ferruginous quartzites (BHQ)?
Canadian experts have an explanation. According to Derek Wilton, Professor of geology at Memorial University in St John, New Foundland, banded iron formation-hosted gold deposits consist of gold intergrown with quartz and or sulphide minerals in deformed and structurally complicated iron-rich sedimentary rocks. In general, most geologists would define these deposits as a variety of the mesothermal lode gold type. These deposits mainly occur within the basis of the mineralogy of the iron-rich layers: if the iron-rich layer is dominantly magnetite-hematite, then the BIF is termed oxide facies (a sedimentary term meaning a distinctive group of characteristics that distinguish one sedimentary unit from another); if the layer is composed of pyrite and or pyrrhotite (iron sulphides), then the BIF is called sulphide facies. There are also carbonate-and silicate-facies BIFs. All BIFs are classified as chemical sediments which mean that they formed through chemical precipitation from seawater on the sea floor. Other sedimentary textures in the BIFs suggest deposition in shallow water on submarine continental shelves. Gold occurs as native (free) gold intergrown with pyrite and /or pyrrhotite; arsenopyrite and /or magnetite are also present in some deposits. Archean-aged greenstone belts, though some are Early Proterozoic. Greenstone belts are linear volcanic and sedimentary centres that are engulfed and completely surrounded by granitic-gneissic basement rocks. Quartz, in the form of crosscutting veins is also a common alteration mineral and, most typically, the gold is intergrown with sulphides in the quartz veins. Chlorite is a common alteration product of silicate minerals here. Most generally, BIF-hosted gold deposits are thought to form by the reaction of auriferous and sulphur-bearing hydrothermal fluids with the iron oxide (or sulphide) in country rocks causing precipitation of gold and sulphides. The gold is present in quartz veins or the immediate wall rock, wherein the precipitation reactions occur."
Our observations were consistent with the above with detection of hematite, Magnetite, Auriferous chert, etc, along with breathtakingly beautiful forms of gold which may be unique to Goa.
(To be concluded)