非均匀物性条件下多尺度窗口修正法换算磁源重力异常及在寻找DSO的应用

摘要

The Direct-Shipping Ore (DSO) is a kind of high-grade iron-rich ore.The Sokoman iron formation with low iron content is of high density and strong magnetism,causing high gravity and magnetic anomalies in the Schefferville mining district,central Labrador Trough in Canada.While the leached enrichment of hematite and goethite (also called DSO) with high iron content is featured by high density and weak magnetism,causing only high gravity anomalies.Conventional filter algorithms cannot extract the magnetic and gravity anomalies arising from DSO.Based on the Poisson equation,we propose a magnetic reduction to the pseudo-gravity anomaly.It transforms magnetic fields into gravity anomalies,then compares the results with gravity observations.The residual gravity anomalies arising from only high-density and non-magnetic DSO are derived.The residual anomalies are interpreted by density inversion and 2.5D interactive inversion.Although the Poisson formula was proposed for a long time,it is used only in qualitative analysis of gravity and magnetic data so far.This paper derives classical Poisson formula in the condition of non-uniform density and magnetic properties,then realizes its process,and presents magnetic field reduction to the gravity field using multi-scale linear regression analysis by moving-windows.The principles of mathematics in this formula can quantify the magnetic and gravity inversion and interpretation.Finally,the pseudo-gravity reduction using multi-scale linear regression analysis by moving-windows is adopted to successfully delineate the DSO with high-density and low magnetism from the Sokoman iron formation in the Schefferville mining district,central Labrador Trough in Canada.%DSO (Direct Shipping Ore,直运块矿)是一种高品位的富铁矿.在加拿大拉布拉多(Labrador)地槽谢菲尔威利(Schefferville)铁矿成矿带,含铁建造苏克曼(Sokoman)组地层全铁含量低、具高密度、强磁性,能够引起高重力异常与高磁异常;而风化淋滤后富集的赤铁矿和针铁矿等(也称DSO)全铁含量高,具高密度、无磁性,仅能够引起高重力异常.采用一般的滤波方法不能提取DSO的重、磁异常.本文采用基于泊松(Poisson)公式的磁场换算磁源重力异常(pseudo-gravity anomaly)方法,由磁场换算磁源重力异常,再与实测重力异常对比,得到纯粹由高密度、无磁性的DSO产生的剩余重力异常,对剩余重力异常采用密度成像与2.5D反演方法解释DSO.泊松公式虽然提出时间很长,但迄今为止仅仅用在资料解释中的定性分析,本文推导并实现了密度磁性非均匀条件下经典泊松公式的形式与实现过程,提出了多尺度窗口滑动线性回归修正的磁场换算磁源重力异常方法,使该公式的数学原理能够对重、磁异常的反演解释定量化.最后本文将多尺度窗口滑动线性回归修正的换算磁源重力异常方法用于加拿大拉布拉多地槽谢菲尔威利铁矿成矿带铁矿勘探,较好地解决了寻找高密度、无磁性DSO的问题.