Stand on a bauxite plateau in Raigad and you are standing on the end product of one of geology's slowest chemical experiments. The rock beneath your feet began as lava. Rain, heat and time turned it into an aluminium ore.
It starts with the Deccan Traps
Around 66 million years ago, enormous volcanic eruptions spread layer upon layer of basalt across western and central India. These flows, known as the Deccan Traps, built the plateaus and stepped hills of the Western Ghats and the Konkan coast.
Basalt is rich in aluminium, but that aluminium is bound into feldspars and other silicate minerals alongside silica, calcium, magnesium, sodium and iron. To become an ore, almost everything except the aluminium and iron has to go.
Weathering does the refining
When basalt sits under a hot, wet climate, rainwater slowly attacks its minerals. The process is called lateritisation, and it works in stages.
- Feldspars and other silicates break down into clay minerals, mostly kaolinite.
- Soluble elements, including calcium, sodium, potassium and magnesium, are carried away in groundwater.
- With heavy rain and good drainage, even the silica in the clay is slowly leached out.
- What remains is enriched in the least mobile elements: aluminium, which crystallises as gibbsite, and iron, which forms goethite and hematite.
The Konkan's intense monsoon and its well-drained plateau tops are close to ideal for this. Water passes through quickly, so dissolved silica is carried away rather than redeposited.
The profile you find when you drill
Because weathering works from the surface down, a drill hole through a lateritic deposit passes through recognisable layers. A typical Konkan profile, like the one shown on our home page, reads from the top:
| Layer | What it is | Why it matters |
|---|---|---|
| Topsoil | Organic soil and roots | Stripped and banked for reclamation |
| Laterite cap | Hard, iron-rich crust | Overburden, removed to reach ore |
| Bauxite | Gibbsite-rich ore zone | The horizon that is mined and graded |
| Lithomarge | Soft, kaolin-rich clay | Too much silica; the floor of mining |
| Basalt | Fresh parent rock | Where the process began |
Thicknesses vary from hill to hill, which is why grid drilling and sampling come before any mining plan. We explain how to read a core in reading a bauxite drill core.
Why Konkan bauxite is gibbsitic
Lateritic bauxites that have never been deeply buried or heated keep their aluminium as gibbsite, the most easily refined form. That matters to buyers: gibbsite dissolves in the Bayer process at lower temperatures than boehmite or diaspore, which reduces energy costs at the refinery. Our article on gibbsite, boehmite and diaspore covers the differences.
Why grade varies across a deposit
Weathering is never perfectly even. Ore close to old drainage channels may be more thoroughly leached and higher in alumina. Patches near the lithomarge can carry more clay and therefore more silica. Iron can concentrate in the cap. This variability is normal, and it is the reason a mine grades its ore rather than selling run-of-mine material as a single product.
At Minequor, on-site crushing, screening and grading let one ore body supply metallurgical, refractory and cement grades, with each lot sampled twice before dispatch.
The takeaway
Konkan bauxite is the product of volcanic basalt, a monsoon climate and tens of millions of years of patience. Understanding that history explains its strengths, chiefly gibbsitic alumina, and its challenges, chiefly variability in silica and iron, which good grading is designed to manage.