Where Diamonds Are Found: Geology of Diamond Deposits

Diamonds reach Earth's surface through specific geological pathways. Understanding these helps locate deposits:

💎 Primary Sources: Kimberlite Pipes

• Carrot-shaped volcanic conduits from 150+ km depth (mantle)
• Rapid magma ascent preserves diamonds (otherwise convert to graphite)
• Erode over millions of years → surface exposure
• Major mines: Jwaneng (Botswana), Orapa (Botswana), Venetia (SA), Udachny (Russia), Diavik (Canada)

🌊 Secondary Sources: Alluvial Deposits

• Rivers/streams erode kimberlite → transport diamonds downstream
• Concentrate in gravel beds, terraces, paleo-channels, coastal plains
• Namibia's Atlantic coast, Sierra Leone, DRC, Brazil, India (historic)
• Easier/cheaper to mine (no blasting); but dispersed, variable grades

🌋 Rare Primary: Lamproites

• Similar deep-origin volcanic rocks (Argyle, Australia — closed 2020; Ellendale)
• Different mineralogy; can host diamonds

🔍 Exploration Indicators

• Indicator minerals: garnet (pyrope), ilmenite, chromite, olivine, diamond itself
• Geophysics: magnetic, electromagnetic, gravity anomalies
• Glacial till sampling (Canada, Scandinavia)

Commercial viability requires: sufficient grade (carats/ton), stone size/quality, infrastructure, stable jurisdiction. Only ~1% of kimberlites are economic.