The Orapa kimberlite field of Botswana is one of the world’s major diamond producing regions. Within this field, there are several small kimberlite pipes that have not been completely explored in terms of their lateral extent, depth, and diamond potential. Two such pipes, BK54 and BK55, were found during a ground gravity and magnetic survey, and subsequent drilling confirmed the presence of kimberlite material. To determine the physical properties of these pipes, their lateral extent, depth, and thickness were estimated using a gravity and magnetic analysis and 2.5D and 3D modeling. Tilt derivatives of the magnetic data indicated that BK54 has a northwest-trending elliptical shape and BK55 has a roughly circular shape. Residual gravity anomaly maps indicate that BK54 does not have a density anomaly whereas BK55 is associated with a gravity maximum. The 3D gravity and magnetic inversion modeling constrained by magnetic susceptibility measurements indicates that BK54 is smaller in volume than BK55 and that neither pipe is thicker than 125 m. The difference in shape and the lack of a gravity anomaly over BK54 implies a different formation mechanism for each kimberlite pipe. Although several mechanisms are suggested, BK54 may have formed by a more explosive eruption producing more tuffistic material in the crater and diatreme facies. The gravity and magnetic analysis also found that the kimberlite pipes, while small, are larger in extent than was determined by drilling and warrant additional drilling to determine their economic potential.

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博茨瓦纳中北部金伯利岩的磁和重力研究

博茨瓦纳的Orapa金伯利岩田是世界主要的钻石产区之一。在这个领域内，有几条小的金伯利岩管道，它们的侧向范围，深度和钻石潜力尚未得到完全研究。在地面重力和磁力测量中发现了两个这样的管道BK54和BK55，随后的钻探证实存在金伯利岩材料。为了确定这些管道的物理特性，使用重力和磁性分析以及2.5D和3D建模估算了管道的横向范围，深度和厚度。磁数据的倾斜导数表明BK54具有西北趋势的椭圆形，而BK55具有大致圆形的形状。残余重力异常图表明BK54没有密度异常，而BK55与重力最大值相关。受磁化率测量限制的3D重力和磁反演模型表明，BK54的体积小于BK55的体积，且两个管道的厚度均不超过125 m。BK54的形状差异和重力异常的缺乏暗示着每个金伯利岩管道的形成机理都不同。尽管提出了几种机制，但BK54可能是由更具爆发力的喷发形成的，在火山口和异常岩相中产生了更多的凝灰岩物质。重力和磁力分析还发现，金伯利岩管虽然较小，但其范围比通过钻孔确定的范围更大，因此需要进行额外的钻孔以确定其经济潜力。