Nandkumar M. Kamat
Goa occupies a crucial segment of the Western Dharwar Craton (WDC), a geological province that has been the cradle of some of India’s most famous gold-bearing belts in neighbouring Karnataka.
In Karnataka, the Kolar, Hutti, and Gadag belts have long been recognised for their primary, lode-type gold mineralisation, hosted mainly in quartz veins and massive sulphide zones. Goa’s case, however, is fundamentally different. Here, the mineralisation is overwhelmingly secondary — gold formed not just in deep crustal hydrothermal systems, but by supergene enrichment processes acting for millions of years on lateritised Banded Iron Formations (BIFs) and associated ferruginous lithologies. This secondary gold is not evenly spread; it is patchy, microscopically fine, and locked within the mineralogy of the iron-rich host.
Published studies, based on years of field sampling, laboratory microscopy, and advanced spectrometry, have described three principal modes of occurrence. First is free-milling particulate gold, generally under 50 microns in size, liberated during controlled size reduction and concentrated in heavy mineral fractions. Second is gold bound as sulphide phases, intimately associated with pyrite or arsenopyrite bands within Banded Magnetite Quartzite (BMQ) and Banded Hematite Quartzite (BHQ). Third is gold complexed with silica in cherty iron ore, occurring in auriferous quartz visible under reflected-light microscopy. In each case, the gold is closely tied to the original microstructures of the host rock, requiring precise liberation techniques before analysis.
These forms have been confirmed by scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX), which shows clear spatial coincidence between gold and sulphur peaks, and by inductively coupled plasma atomic emission spectroscopy (ICP-AES) carried out under strict matrix-matched calibration conditions. The grades detected in these controlled conditions range from sub-ppm to well over 40 ppm in certain micro-enriched bands — values that, if reproducible on a bulk scale, would be economically interesting.
Yet this gold is not easily revealed. Both iron and manganese in ores create powerful spectral interference in techniques such as ICP-AES and atomic absorption spectroscopy (AAS), potentially masking the gold signal. Laboratories that have successfully detected gold in Goan material have done so by calibrating their instruments with synthetic standards matching the iron-manganese matrix, applying spectral deconvolution algorithms, and working with powdered samples milled to below 105 microns to ensure the gold-bearing fraction is not diluted by barren coarse material. By contrast, if a laboratory uses coarse, unclassified samples, applies standard calibration designed for low-iron ores, or skips pre-treatment steps needed to liberate sulphide-bound or silica-bound gold, the result can be a clean “not detected” — a false negative.
Fire assay, though widely seen as the definitive test for precious metals, is also vulnerable here. Unless the flux recipe is modified to break silica-gold bonds in chert, or unless sulphides are oxidised prior to fusion, a significant fraction of the gold will remain locked in the slag. Solvent extraction followed by AAS can also fail if complexing agents in the sample bind gold too strongly to be recovered under the extraction conditions used.
The distribution of secondary gold in Goa’s BIF-hosted systems is notoriously heterogeneous. Even within a single outcrop, adjacent fragments may differ by an order of magnitude in gold content. Enriched pockets may be no larger than a few centimetres, while the surrounding material is barren. Sampling programmes that composite material from large areas or avoid micro-localities of enrichment are guaranteed to dilute the gold content below detection limits. This is why protocols in the published literature emphasise selective sampling of visually distinctive lithologies, preparation to fine particle size, and concentration of heavy mineral fractions prior to analysis. Here lies the crux of the matter.
The Government of Goa, through its Directorate of Mines and Geology, has publicly indicated interest in “scientifically” collecting and testing ore samples to resolve the question of whether gold occurs in the state’s ores. On paper, this sounds like a welcome step. But unless the sampling and analytical protocols incorporate the lessons from the peer-reviewed literature, the outcome is almost predetermined. A programme that uses coarse unclassified samples, single-lab analysis without matrix-matched calibration, and no independent verification will almost certainly report “no gold detected.” Such a result would not disprove the existence of gold; it would merely prove that the method chosen was incapable of finding it.
This is not a hypothetical risk. The history of gold exploration is full of cases where deposits were declared barren by one generation, only to be proven rich by another. In Western Australia’s Yilgarn Craton, banded iron-hosted gold deposits were overlooked for decades because the exploration methods were copied from quartz-vein gold contexts. In South Africa’s Witwatersrand Basin, gold in iron-rich conglomerates went unrecognised because the analytical focus was on uranium. In Brazil’s Quadrilátero Ferrífero, gold in itabirite was missed because iron ore companies assumed that iron-rich lithologies could not carry payable gold. In all these cases, the shift from “barren” to “rich” came not from geological change, but from methodological change — understanding the mineral associations and adjusting the analytical protocols accordingly.
In Goa’s case, the danger is compounded by the political and economic stakes. The iron ore industry dominates the mining discourse, and any shift in attention toward gold or other strategic metals could disrupt entrenched interests. A government-issued “no gold” verdict, especially if framed as the result of “more scientific” testing, would be a powerful tool to discredit published research and dampen public interest. This makes transparency not optional, but essential. A credible and tamper-proof sampling programme in this context would require multiple safeguards. The sampling must be carried out in the presence of independent observers, with clear documentation of the geological context and GPS coordinates. Each sample must be immediately split into at least three identical sealed sub-samples, with one retained by the sampling team, one sent to the government’s chosen laboratory, and one sent to an independent facility with a proven track record in high-iron matrix gold analysis. The preparation stage must include controlled crushing and milling to <106 microns, with periodic checks for particle size distribution. Analytical methods must be selected based on their ability to overcome iron and manganese interference, with full reporting of calibration curves, blanks, standards, and recovery rates. Gravity separation or heavy mineral concentration steps should be used wherever relevant, and all residual tailings should be retained for possible re-checking. Without these measures, any “negative” result will be open to suspicion, and rightly so.
The peer-reviewed literature on Goa’s ores has already provided the mineralogical maps, the analytical recipes, and the proof-of-concept results. Ignoring these is not just a scientific lapse — it risks locking the state into a false narrative about its geological potential. If the government’s goal is genuinely to resolve the gold question, then it must design a testing programme that can detect gold if it is there, not one that is structurally biased toward not finding it.
Ultimately, this is a test not of the ores, but of the system. A transparent, multi-laboratory, protocol-driven investigation would put the matter beyond dispute, whichever way the results fall. A closed, single-pathway, unverified programme will prove nothing except the determination of its designers to maintain the status quo.
Goa’s choice is simple: it can join the long list of regions where mineral wealth was missed for want of the right method, or it can lead by example in showing how science, done properly, serves the truth.