RE: Makes you wonder14 Apr 2026 10:22
To prove a diatreme-shaped electromagnetic (EM) and magnetic anomaly is a kimberlite pipe, initial drilling must move beyond geophysical interpretation to confirm the presence of kimberlitic rock and, crucially, to obtain samples for mineralogical, petrographic, and petrological analysis.
Initial Drilling Requirements to Prove Kimberlite:
• Diamond Core Drilling (DDH): This is the primary and essential method for initial testing, as it provides a continuous, high-quality rock sample for geological logging.
o Positioning: The first hole should be targeted directly into the center or the highest-intensity part of the magnetic/conductivity anomaly.
o Inclination: Drilling should ideally be vertical for smaller pipes to maximize intersection time, or at an angle (-45° to -60°) to cut across the estimated boundaries of the diatreme if the pipe diameter is larger.
o Core Size: Standard Core size (e.g., HQ or NQ) is used, although large-diameter drilling (RC) is needed later for bulk sampling (diamond grade).
• Initial Drilling Strategy:
o "Twin" the anomaly: At least one, but preferably two or three, strategically placed diamond drill holes (DDH) should be used to confirm the pipe exists, assess its vertical and horizontal extent, and identify the facies (crater, diatreme, or root).
o Depth: Drilling must penetrate through the overburden into the bedrock, ideally continuing for at least 50-100 meters within the suspected kimberlite to confirm it is not just a thin sheet or dike.
Key Objectives of Initial Drilling:
1. Lithological Identification: Confirm the rock is kimberlite (magmatic/fragmental textures, macrocrystic olivine) rather than other rock types (e.g., lamproite, basalt, gabbro).
2. Facial Analysis: Distinguish between crater-facies (volcaniclastic), diatreme-facies (tuffisitic), or hypabyssal kimberlite.
3. Confirming Geometry: Drilling validates the magnetic/EM-interpreted shape and size of the pipe (e.g., circular vs. elongated).
4. Indicator Mineral Identification: The core is logged for the presence of "diamond indicator minerals" (G10 pyrope garnets, picroilmenite, chromite).
Follow-Up After Initial Drilling:
Once the pipe is confirmed by drilling (and often petrography), if indicator minerals or geological characteristics are promising, large diameter Reverse Circulation (RC) drilling (e.g., 609–914 mm) is used to obtain a bulk sample for diamond grade analysis.