Remote Sensing for Chromite Exploration: A Practical Guide Using ASTER and Sentinel-2 in Pakistan's Ophiolite Belts

By Sufyan · 2026-07-18 · 4 min read

Chromite is stubborn.

I mean that literally — the mineral itself is dense, chemically boring in the good way (chromium locked in a tight spinel crystal), and it hides inside ultramafic rocks that all look the same from a helicopter. Ask any field geologist who's walked the Muslim Bagh ophiolite in the July heat. You can stand ten meters from a podiform lens worth crores and miss it because the host rock — dunite, harzburgite, serpentinite — looks identical for kilometers.

So how do we find it from 786 km up?

Honestly, when I started GeoMine AI I thought Sentinel-2 alone would do most of the work. I was wrong. Sentinel-2 is brilliant for a lot of things but chromite exploration isn't really one of them, not directly. You need ASTER. And you need to know what you're actually looking at when you stack them.

Let me walk through what we do at geomines, and what a mine owner or exploration manager should demand from any consultant handing over a "satellite report."

Why ASTER Still Wins for Chromite (Even Though It's Old)

ASTER launched in 1999. The SWIR sensor died in 2008. And yet it's still the single most useful public dataset for chromite exploration Pakistan-wide. Here's why — the pre-2008 SWIR bands (specifically bands 5, 6, 7, 8) sit exactly on the absorption features of Mg-OH bonds. Serpentine, talc, chlorite — the alteration halo around podiform chromite deposits — lights up on band ratios like 7/5 and (5+7)/6.

That's the trick. You're not seeing the chromite ore itself. Chromite is nearly featureless in VNIR-SWIR. What you're seeing is the serpentinized envelope that almost always wraps podiform bodies in ophiolites.

We run three ratios by default on any ophiolite target:

Stack those as RGB and the Muslim Bagh complex practically draws itself. Same with the Waziristan ophiolite, the Khost-Kurram belt across the border spillover zones, and the Bela ophiolite down in Balochistan. Zhob valley too — though the vegetation there gives us more noise than I'd like.

The thermal bands (TIR, 90m resolution) are useful for a second pass. Chromite-rich zones show subtle emissivity contrasts because of the higher chromium and iron content. Coarse, but real.

Where Sentinel-2 Actually Earns Its Keep

Sentinel-2's 10m resolution beats ASTER's 15m, and the revisit is every 5 days versus ASTER's occasional targeted acquisition. So we use it differently.

First, structural mapping. Chromite pods sit along shear zones, listwaenite alteration trails, and the basal thrust of the ophiolite sheet. Sentinel-2's sharper resolution lets us trace lineaments and small offset patterns that ASTER smears. In the Muslim Bagh sheet we've mapped shear-parallel drainage anomalies at 20m spacing that correlate with known chromite workings from the 1970s Pakistan Mineral Development Corporation reports.

Second, iron oxide indices. Bands 4 and 2 give you a decent ferric iron ratio. Not as clean as ASTER but with weekly refresh you can watch how alteration signatures change across dry and post-monsoon acquisitions — sometimes rain washes surface dust off and a signature that was invisible in April pops in October.

Third — and this one people forget — Sentinel-2 is your reality check. ASTER pixel says "serpentinite alteration here." You pull the same coordinate in Sentinel-2 at 10m and see it's a shadow from a ridge, or a road cut, or someone's goat pen. This happens more than any consultant will admit.

I got burned on this early. 2022, a target in Khanozai — beautiful ASTER anomaly, cluster of Mg-OH hits, I was ready to send a team. Sentinel-2 close-up showed it was a dry riverbed with concentrated dust from a marble quarry upstream. Now every target goes through a Sentinel-2 sanity pass before it touches a field plan.

What a Real Chromite Workflow Looks Like

Here's roughly how a geo mine target gets built at GeoMine AI, start to drill-ready:

  1. Regional ASTER mineral mapping across the full ophiolite belt Pakistan segment of interest — usually a 40 x 60 km tile
  2. Ultramafic footprint extraction using Mg-OH and ferric ratios
  3. Sentinel-2 structural overlay — lineaments, shear zones, drainage anomalies
  4. SRTM DEM slope and curvature analysis (podiform bodies often sit on specific structural positions within the mantle sequence)
  5. SAR coherence for surface disturbance — old workings, recent digging, access tracks
  6. Cross-reference with any GSP (Geological Survey of Pakistan) legacy mapping
  7. Rank targets by combined score, then ground-truth the top 8-12

That last step is non-negotiable. Remote sensing chromite work without ground verification is just a pretty map. I've seen investors handed 30-page reports full of ASTER ratios with zero field validation and asked to commit 4 crore to drilling. Please don't.

A proper breeze geo mineral analysis workflow — the kind we build into every GeoMine report — should end with a field checklist, not a conclusion slide. Coordinates, expected mineralogy at each point, photos to take, samples to collect, and a clear "if we see X here, drill; if we see Y, walk away."

One Thing I'd Tell Any Mine Owner Reading This

Don't pay for a satellite study that only uses one sensor. If your consultant's report is 90% Sentinel-2 with a token ASTER slide, they're cutting corners. Chromite needs SWIR. Full stop. And if the report has no SAR and no DEM analysis, they've skipped half the physical evidence sitting freely on Copernicus and USGS servers.

The data's public. The processing isn't magic. What separates a useful report from an expensive PDF is whether the person building it has actually stood on a chromite outcrop in Muslim Bagh and knows what the alteration smells like when you break a fresh sample.

Anyway — that's the honest version. Questions about a specific block? You know where to find me.

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