A Gravity Survey is a geophysical exploration technique that measures variations in the Earth's gravitational field across a survey area to detect subsurface density contrasts between different rock types, geological structures, mineral deposits, and voids. The survey uses sensitive instruments called gravimeters or gravity meters to measure gravitational acceleration, with results expressed in milligals (mGal) or gravity units (g.u.).
Variations in measured gravity, known as gravity anomalies, are corrected for latitude, elevation, terrain, and instrument drift before interpretation. In mining exploration, gravity surveys are valuable for mapping subsurface geology without drilling. In iron ore exploration, the high density of iron ore compared to surrounding rocks produces strong positive gravity anomalies that can delineate ore bodies at depth.
In diamond exploration, gravity surveys help identify kimberlite pipes — the primary host rock for diamonds — which are typically less dense than the surrounding country rock and therefore produce negative gravity anomalies. In bauxite exploration, gravity surveys may be used to understand the structural geology controlling bauxite distribution. In gold exploration, gravity data helps map greenstone belts, fault zones, and intrusions that may host mineralisation.
Gravity surveys can be conducted on the ground by field teams or from the air using airborne gravity gradiometry systems mounted on aircraft, which allow rapid coverage of large and remote areas. Data is typically integrated with magnetic, seismic, and drilling information.