By Nandkumar M Kamat
I don’t wish to reveal the quantity of exploitable gold from Banded Hematite Quartzite (BHQ) derived mining rejects of Goa or estimates of gold lost due to faulty, outdated policies.
This is a colossal national loss considering the present economic recession. About auriferous rock formations, ores, minerals, sands, soils, sediments-the standard policy of central government till 1987 and state government till date is to maintain total silence and follow the four-century-old Portuguese precautionary policy.
The Portuguese policy has been described aptly by the famous 16th century Dutch traveller, Jan Huyghen van Linschoten, who visited Goa in 1583 and wrote an account of his travel, ‘The Voyage of John Huyghen van Linschoten to the East Indies’, published for the first time in English in 1885. He had written in 1583 after touring Goa, “The land itself is very stony and dry having a kind of red earth so that some Italian Alchemists have promised to get copper and gold out of the same, which neither the king nor viceroy would ever consent unto fearing least the report of such treasure would be occasion of greater trouble unto them by their enemies that are around them.” The Portuguese king and his viceroy in Goa were scared of a gold rush and attack from enemies.
The same concerns continue but facts are facts. Even without a gold rush, Goa is losing gold and exporting ores with gold content. The answer to the possible question – how did we find gold in BHQ ore rejects? - is simple. You need to specifically look for gold with an open mind and not from purely a miner’s, a geologist’s or a geochemist’s or an engineer’s angle. Besides, one needs to follow the latest global trends in the micro prospecting of gold. One needs to be sceptical about absence of data on geochemical analysis of gold in Goa because there is a conspiracy of silence on this subject owing to the value of the metal. The logic should have been simple. If the auriferous rocks of Goa are similar to Chitradurga then there would be gold. There had been enough hints in chapters of the monograph ‘Natural resources of Goa’ by late O A Fernandes. There is a lot of information about gold content in tropical laterite and saprolite. But when a geologist like Mike Widdowson gives a detailed geochemical analysis of lateritic profile in Tiswadi (chapter 4 in the above book) we wonder about the elimination of any possible data on gold content. This is despite samples being taken from surface to a depth of 34 metres. Why did he find 16 other trace elements more important than gold despite the knowledge of gold content of laterites?
The conspiracy of silence extends to the Geological Survey of India-GSI. A paper published in June 2009 on soil and stream, based on geochemical mapping of Goa, mentions about geochemical analysis of 200 soil or lateritic samples and 654 stream sediment samples. They analysed 34 trace elements by Plasma Quad PQ1 ICP-MS at National Geophysical Research Institute (NGRI) laboratory. They also claimed to have analysed 152 stream sediment samples from southern parts of Goa for gold by Atomic Absorption Spectroscopy (AAS). So far so good. But the paper is totally silent on their gold analysis. So we are left in the dark about gold content in stream sediments of 152 samples from South Goa.
What did happen to this AAS based data on gold in streams of South Goa? Did they pass on the information to the Goa government or transfer it to private mining companies directly? If the gold content in these stream sediments was not detected then the authors should have mentioned it in the paper. This is a classic case of public-funded government publications where analysis is mentioned but results are hidden. I strongly suspect that the stream sediments were proved positive for gold and therefore the GSI took a decision to omit the data from the paper consistent with the old Portuguese policy.
There is a degree of hesitation among traditional geologists in embracing relatively novel areas like geomicrobiology, geomycology, geobotany and nanobiotechnology. Goa’s mining industry needs a holistic multidisciplinary knowledge based on geomicrobiological paradigm shift because everywhere one looks there are microbiogenic minerals.
There are ancient petrified stromatolites in upper reaches of Mahadayai basin and marine fossil beds in coastal areas. Almost all ores have chemolithotrophic microbes. Available data reveals that from 1951 to 2011, Goa exported about 800 million MT of iron ore. A large portion of the exports have come from BIF-BHQ zone of North Goa. This may account for more than 500 million MT. Since ores are not subjected to gold analysis it is difficult to quantify how much has been exported.
The iron ore rejects in mines of Goa comprise low grade lumpy ore, low grade aluminous powdery ore, low grade siliceous powdery ore, low grade screen fines and dressed rejects. From the billion MT rejects left behind, again, it is difficult to estimate total quantity of BHQ overburden. According to Professor Wilton, Canadian expert on gold in BIF, in general Banded Iron Formations (BIFs) contain between 4 and 30 grams of gold per tonne; at least in his country. The BHQ rejects don’t have iron content less than 51 percent.
BHQ has been analysed by Raikar and Sahu for silica, aluminium, titanium, manganese, phosphorous, calcium, magnesium and trace elements like chromium, cobalt, nickel, copper, zinc and lead. Sahu and Saraf also reported lead, chromium, zinc, cobalt, nickel, copper and strontium in BHQ. However, since there was no knowledge of the possibility of Auriferous chert and bacterioform gold within BHQ, no specific attention was paid by any geochemist to detect gold either by XRF, Atomic Absorption Spectroscopy or Neutron Activation Analysis. In dead dumps there would be natural enrichment of the heavy gold fraction as lighter fraction is eroded due to rainfall. In active dumps the gold content is difficult to isolate.
Overall, both dead and active mining reject dumps in North Goa can yield enough quantities of gold, exceeding the export value of the Iron ore. It doesn’t make any economic sense to keep these dumps idle without separation of the gold that is required by national economy. But the state government is only focussed on iron, manganese and aluminium. The extraction of these ores has ruined Goa. From the ruins the earth goddess has sent a golden blessing. From Advalpale to Usgao there is enough gold in mining rejects to transform the economy and restore the traumatised ecology if our government wakes up and acts. (Concluded)