Gravity Survey for Mineral Exploration: When It's Actually Worth the Money

A gravity survey costs more than most junior explorers expect. I've seen quotes from $18,000 to $74,000 for a single mid-sized block in Chagai, and that's before you pay the interpreter who actually knows what the numbers mean.

So is it worth it?

Honestly, sometimes yes. Sometimes absolutely not. And the answer almost never has to do with the mineral you're chasing — it has to do with what's sitting on top of your target and how deep you think the orebody is.

Let me explain how I think about this, because I've burned money on gravity work that told me nothing, and I've also spent $22,000 on a ground gravity campaign that saved me from drilling a dry hole.

What a Gravity Survey Actually Measures

Gravity survey methods measure tiny variations in Earth's gravitational field. We're talking microgals here — units so small that a person walking past the gravimeter can mess up your reading. The instrument picks up density differences in the rock below your feet. Dense stuff (massive sulphides, chromite, iron oxides, ultramafic intrusions) pulls harder. Lighter stuff (granite, sediments, alteration zones, voids) pulls less.

That's the whole physics in one paragraph.

The interesting part is what you do with it. There are basically three flavors of gravity work you'll encounter in Pakistan:

Ground gravity — someone walks a grid with a gravimeter, stops every 50 to 200 meters, takes a reading. Slow. Expensive. Most accurate. This is what you commission when you've already narrowed down a target zone.

Airborne gravity — flown on fixed-wing or helicopter. Covers huge areas fast. Resolution is lower. Good for regional reconnaissance over a 500 km² license.

Satellite-derived gravity — from missions like GRACE and GOCE. Resolution is poor (think tens of kilometers), but it's free and good for understanding crustal-scale structure. We pull this into our reports at GeoMine AI as a backdrop layer when we're building regional context.

For gravity survey mineral exploration on a typical exploration license in Balochistan or Gilgit Baltistan, ground gravity is what people mean when they say "we need a gravity survey."

When It's Worth the Money (And When It Isn't)

Here's the thing. Gravity works brilliantly for some targets and badly for others.

It works well for:

• Massive sulphide bodies (copper-gold porphyries with dense sulphide cores)
• Chromite pods in ultramafic host rocks — though the density contrast can be tricky
• Iron ore
• Kimberlite pipes (negative anomalies, usually)
• Structural mapping where you need to find a buried contact between two rock types of different densities

It works poorly for:

• Lithium in pegmatites (almost no density contrast with surrounding granite)
• Gold-only systems with low sulphide content
• Most emerald and gemstone targets
• Shallow disseminated deposits where the contrast is too small to detect

I used to think gravity was useful on almost any project. I got that wrong. On one of my mines in Skardu — a marble property — someone convinced me to commission a small gravity grid. We spent around 11 lakh PKR. The data was clean, professionally collected, and told us absolutely nothing we didn't already know from surface mapping. Marble against marble. No contrast.

The lesson: ask the density question first. If you can't articulate why two rock units on your property would have different densities, don't pay for gravity.

How Interpretation Actually Works

This is where most projects fall apart. The data collection is the easy part. Interpretation is where geophysicists earn their fees.

A raw gravity reading is useless. The data goes through corrections — for tides, latitude, elevation (free-air), surrounding rock mass (Bouguer), and terrain. What you end up with is called a Bouguer anomaly map. Then someone takes that map and applies filters: regional-residual separation, upward continuation, derivatives. Each filter pulls out signals at different depths.

The first derivative sharpens contacts. The second derivative shows you edges of buried bodies. Upward continuation suppresses shallow noise and shows you deeper structure.

A good interpreter will hand you back not one map but six or seven, each answering a different geological question.

And here's where satellite data and gravity become genuinely powerful together. At GeoMine AI we routinely overlay Sentinel-2 alteration mapping and ASTER mineral indices on top of Bouguer residual maps. A copper porphyry should show both — a positive gravity anomaly from the sulphide core, and a clay-sericite alteration halo visible from space. When both line up in the same 800-meter window, that's a drill target. When only one shows up, you keep looking.

This is essentially what our breeze geo mineral analysis workflow does — it stacks the geophysical, spectral, and structural evidence layers and tells you where they agree.

My Honest Recommendation for Pakistani Operators

Look, if you're running a mid-size operation in Chagai, Waziristan, or anywhere along the suture zones in the north, here's the sequence I'd actually follow:

Start with satellite. Spend $2,000 to $8,000 getting a proper remote sensing study done across your whole license. That includes ASTER alteration mapping, SAR structural analysis, and DEM-derived lineament work. This narrows a 100 km² license down to maybe three or four target zones of a few square kilometers each.

Then do geological ground-truthing on those zones. Walk them. Sample them. Confirm the satellite signal is real and not just a false positive from soil moisture or vegetation.

Only then commission ground gravity — and only on the one or two zones where you have a real density-contrast hypothesis. A focused 4 km² ground gravity grid in Pakistan currently runs between 14 and 28 lakh PKR depending on access and station spacing. That's money you can justify when it's the third filter in a chain, not the first.

The operators I see wasting money are the ones who commission a 50 km² airborne gravity survey before they've even looked at a Landsat scene. They end up with beautiful data and no idea what to do with it.

Geo mining isn't getting cheaper. But the order in which you spend matters more than the total spend. Satellite first, ground second, geophysics third, drilling last. Skip a step and you're paying for the privilege of being confused at higher resolution.

What targets are you working on right now where you're not sure gravity would help?