Airborne gamma-ray spectrometry inversion signatures of Hicks Dome area
No abstract available.
Illinois↗
Geology topics
Yaoguo Li
Publications and source records attributed to Yaoguo Li.
Chapter 10: Regional- to deposit-scale geologic controls on copper-silver mineralization in the Kalahari Copperbelt, Botswana
The Kalahari Copperbelt in northwestern Botswana is characterized by structurally controlled, stratabound, mineralogically zoned copper-silver deposits hosted along a major redox boundary within a late Mesoproterozoic rift succession. Copper-silver mineralized rocks occur on the limbs and in the hinge positions of regional-scale folds that characterize the Pan-African Ghanzi-Chobe zone fold-and-thrust belt. Regional facies changes along the base of the transgressive marine D’Kar Formation, the host to the majority of mineralized rocks, delineate a series of synsedimentary basin highs and lows. The facies changes were identified through both lithostratigraphic analysis of drill holes and along-strike variations in magnetic lithostratigraphy, a technique that correlates the magnetic fabrics of second vertical derivative aeromagnetic maps with changes in lithostratigraphy. Basin highs controlled the development and distribution of favorable lithostratigraphic and lithogeochemical trap sites for later sulfide precipitation. Major facies changes across the Ghanzi Ridge area straddle a significant crustal structure identified in gravity datasets that appears to have influenced extensional activity during basin development. During basin inversion, the basin highs, cored by rheologically stronger bimodal volcanic rocks, localized strain within mechanically weaker rock types of the Ghanzi Group metasedimentary rocks, leading to the development of locally significant permeability and the formation of structural trap sites for mineralization by hot (250°–300°C), oxidizing, metalliferous Na-Ca-Cl brines. Structural permeability was maintained within trap sites due to silicification and/or feldspar alteration during progressive deformation and associated hydrothermal mineralizing events.
Kalahari Copperbelt↗
Three-dimensional distribution of igneous rocks near the Pebble porphyry Cu-Au-Mo deposit in southwestern Alaska: constraints from regional-scale aeromagnetic data
Aeromagnetic data helped us to understand the 3D distribution of plutonic rocks near the Pebble porphyry copper deposit in southwestern Alaska, USA. Magnetic susceptibility measurements showed that rocks in the Pebble district are more magnetic than rocks of comparable compositions in the Pike Creek–Stuyahok Hills volcano-plutonic complex. The reduced-to-pole transformation of the aeromagnetic data demonstrated that the older rocks in the Pebble district produce strong magnetic anomaly highs. The tilt derivative transformation highlighted northeast-trending lineaments attributed to Tertiary volcanic rocks. Multiscale edge detection delineated near-surface magnetic sources that are mostly outward dipping and coalesce at depth in the Pebble district. The total horizontal gradient of the 10-km upward-continued magnetic data showed an oval, deep magnetic contact along which porphyry deposits occur. Forward and inverse magnetic modeling showed that the magnetic rocks in the Pebble district extend to depths greater than 9 km. Magnetic inversion was constrained by a near-surface, 3D geologic model that is attributed with measured magnetic susceptibilities from various rock types in the region. The inversion results indicated that several near-surface magnetic sources with moderate susceptibilities converge with depth into magnetic bodies with higher susceptibilities. This deep magnetic source appeared to rise toward the surface in several areas. An isosurface value of 0.02 SI was used to depict the magnetic contact between outcropping granodiorite and nonmagnetic sedimentary host rocks. The contact was shown to be outward dipping. At depths around 5 km, nearly the entire model exceeded the isosurface value indicating the limits of nonmagnetic host material. The inversion results showed the presence of a relatively deep, northeast-trending magnetic low that parallels lineaments mapped by the tilt derivative. This deep low represents a strand of the Lake Clark fault.
Alaska↗
Inversion of multichannel geophysical data with projected kernels
Statistical de‐noising methods such as Principal Component Analysis modify data in a way not constrained by physics. In much the same way as frequency‐filtered data must incorporate altered frequency content into numerical interpretation, so must statistically rotated data include the rotation operator in inversion processes. We propose a method of accounting for statistical reduction of data in non‐linear inversions (such as for electromagnetic data) through an incorporation of the rotation operator into the kernels and sensitivity matrix. We show a generalized linear inversion to demonstrate the necessity of rotating the inversion kernels in this abstract and will present a nonlinear parametric example from an unexploded ordnance application.
Conference Paper↗