This chapter is devoted to discussing the updated findings from recent work completed at the Sukari Gold Deposit, located within the Arabian-Nubian Shield of Egypt. It delves into the local geology and the primary hosts to gold, emphasising the granodiorite-hosted orogenic nature of the deposit. The chapter examines the complex interplay of thrusting, shearing, and folding relations and their impact on the spatial distribution of gold. It also explores the controls on gold emplacement within the structural framework of the deposit, underlining the significance of the deposit-scale alteration and gold paragenesis. Further, the geochemistry of the host granodiorite is analysed to reveal new details bearing on the genesis of the deposit. The study classifies the Sukari Gold Deposit within the broader context of orogenic gold deposits, highlighting its unique characteristics and implications for exploration and mining strategies in similar geological settings. The chapter aims to offer a comprehensive understanding of the deposit’s geology, structural evolution, and the factors influencing gold mineralisation, contributing to the ongoing development and optimisation of mining operations at Sukari. The geometry of the deposit and the ingress of gold-bearing fluids are products of a tectonic history comprising two principal deformation events, D1 and D2, that sponsored development of a major permeability framework in each event. Significantly, D2 was not recognized previously and has been responsible for reactivation of the early-formed D1 permeability framework, allowing for the introduction and deposition of gold structurally late during D2 sub-vertical shortening. Much of the deposit architecture was established during sub-horizontal shortening associated with D1 of the Sukari concession. This event also sponsored a major permeability-forming event that resulted in a series of wallrock alterations and generations of veins, including the distinctive milky white quartz vein population that is a common host to gold mineralisation. Notably, the milky quartz veins are significantly older than gold mineralisation, acting as competent hosts that were overprinted much later. Emplacement of the Sukari granodiorite is envisaged as occurring early in the D1 event. It is impossible to say how much of the current geometry is a product of the original emplacement and how much is a product of tectonic in-slicing into the sequence. Regardless, the presence of the Sukari granodiorite resulted in significant strain partitioning, producing zones of intense strain at the intrusive margins. After a tectonic hiatus, sub-vertical D2 shortening led to reactivation of the D1 permeability framework. Several vein emplacement events, culminating in development of structures hosting late gold-sulphide mineralisation associated with stylolitic textures. Recent construction of geological sections and mapping has allowed modeling of the evolution of the deposit architecture. Importantly, the geometry of gently-dipping structures, e.g. the Osiris Fault can be rationalised in terms of D2 rotation of early-formed D1 structures. A first-pass, detailed geological history for the Sukari deposit has been established, based on the review of underground and open pit exposures, concession-wide outcrops, drill core, and the preparation of 2D and 3D models. This is the first time a complete snapshot of deposit evolution that includes all alteration, structure, lithology, mineralisation, and vein populations has been established. The kinematic evolution of major structures, many of which have accommodated more than one major stage of movement, has been incorporated into the model. D1 is interpreted as comprising west- to northwest-directed transport, consistent with regional tectonic models, and produced east-side-up, sinistral displacements on NW–SE to N-S trending faults. In the latter stages of D2, low-dipping structures such as Osiris have accommodated top-block-north transport. Steeply dipping structures to the west of Osiris, such as the Sukari Transfer Fault (STF), are interpreted as acting as transfer structures that accommodated differential, top-to-the-north transport in combination with vertical shortening. This has removed the necessity for continuity of low-dipping faults to the west of the Sukari Transfer Fault and explains why the deposit-scale F2 folding is overwhelmingly developed to the east of it.

错误:搜索内容不能为空,请输入英文关键词
错误:关键词超出字数限制,请精简
高级检索

Sukari—A Structurally Controlled, Granodiorite-Hosted Orogenic Gold Deposit in the Arabian-Nubian Shield, Egypt

  • Brett Davis,
  • Craig Barker

摘要

This chapter is devoted to discussing the updated findings from recent work completed at the Sukari Gold Deposit, located within the Arabian-Nubian Shield of Egypt. It delves into the local geology and the primary hosts to gold, emphasising the granodiorite-hosted orogenic nature of the deposit. The chapter examines the complex interplay of thrusting, shearing, and folding relations and their impact on the spatial distribution of gold. It also explores the controls on gold emplacement within the structural framework of the deposit, underlining the significance of the deposit-scale alteration and gold paragenesis. Further, the geochemistry of the host granodiorite is analysed to reveal new details bearing on the genesis of the deposit. The study classifies the Sukari Gold Deposit within the broader context of orogenic gold deposits, highlighting its unique characteristics and implications for exploration and mining strategies in similar geological settings. The chapter aims to offer a comprehensive understanding of the deposit’s geology, structural evolution, and the factors influencing gold mineralisation, contributing to the ongoing development and optimisation of mining operations at Sukari. The geometry of the deposit and the ingress of gold-bearing fluids are products of a tectonic history comprising two principal deformation events, D1 and D2, that sponsored development of a major permeability framework in each event. Significantly, D2 was not recognized previously and has been responsible for reactivation of the early-formed D1 permeability framework, allowing for the introduction and deposition of gold structurally late during D2 sub-vertical shortening. Much of the deposit architecture was established during sub-horizontal shortening associated with D1 of the Sukari concession. This event also sponsored a major permeability-forming event that resulted in a series of wallrock alterations and generations of veins, including the distinctive milky white quartz vein population that is a common host to gold mineralisation. Notably, the milky quartz veins are significantly older than gold mineralisation, acting as competent hosts that were overprinted much later. Emplacement of the Sukari granodiorite is envisaged as occurring early in the D1 event. It is impossible to say how much of the current geometry is a product of the original emplacement and how much is a product of tectonic in-slicing into the sequence. Regardless, the presence of the Sukari granodiorite resulted in significant strain partitioning, producing zones of intense strain at the intrusive margins. After a tectonic hiatus, sub-vertical D2 shortening led to reactivation of the D1 permeability framework. Several vein emplacement events, culminating in development of structures hosting late gold-sulphide mineralisation associated with stylolitic textures. Recent construction of geological sections and mapping has allowed modeling of the evolution of the deposit architecture. Importantly, the geometry of gently-dipping structures, e.g. the Osiris Fault can be rationalised in terms of D2 rotation of early-formed D1 structures. A first-pass, detailed geological history for the Sukari deposit has been established, based on the review of underground and open pit exposures, concession-wide outcrops, drill core, and the preparation of 2D and 3D models. This is the first time a complete snapshot of deposit evolution that includes all alteration, structure, lithology, mineralisation, and vein populations has been established. The kinematic evolution of major structures, many of which have accommodated more than one major stage of movement, has been incorporated into the model. D1 is interpreted as comprising west- to northwest-directed transport, consistent with regional tectonic models, and produced east-side-up, sinistral displacements on NW–SE to N-S trending faults. In the latter stages of D2, low-dipping structures such as Osiris have accommodated top-block-north transport. Steeply dipping structures to the west of Osiris, such as the Sukari Transfer Fault (STF), are interpreted as acting as transfer structures that accommodated differential, top-to-the-north transport in combination with vertical shortening. This has removed the necessity for continuity of low-dipping faults to the west of the Sukari Transfer Fault and explains why the deposit-scale F2 folding is overwhelmingly developed to the east of it.