Xinping Cai

Characteristics and dynamic origin of the large-scale Jiaoluotage ductile compressional zone in the eastern Tianshan Mountains, China

Abstract The Jiaoluotage ductile compressional zone (JDCZ) in the eastern Tianshan Mountains, China, developed in volcanic and sedimentary rocks that were deposited in a Carboniferous back-arc basin situated between the Jungar plate and middle Tianshan terrane. The ductile compressional zone, ∼500 km long and 20–50 km wide, consists of a number of east-trending vertical foliation zones that display an augen geometry in plan view and a fan-like geometry in transverse profiles. Ductile compressional deformation has produced pervasive foliation, radial stretching lineations, contemporaneous folds, and various macroscopic to microscopic symmetric structures within the JDCZ. Rotations of most clasts and porphyroclasts are bidirectional. The preferred orientation patterns of the optical axes of calcite and quartz display axial or orthorhombic symmetry. Three kinds of strain patterns have been determined in the JDCZ: apparent flattening, plane strain and apparent constriction. The overall strain character of the JDCZ is ‘cream-cake’ style. The volcanic and sedimentary rocks within the JDCZ were metamorphosed into greenschist facies with temperature of 400–600 °C and pressure of 300–400 MPa. Development of the JDCZ is interpreted as due to N–S coaxial compression caused by the collision between the Tarim plate and the middle Tianshan arc–Jiaoluotage basin–Jungar plate system during the Permian between 270 and 290 Ma.

Fluids double-fracturing genetic mechanism and mineralization of gold-copper of the breccia pipe at Qibaoshan in Shandong Province

After studying the characteristics and special texture of the fluidogenous tectonics, mineral assemblage in the cemented vein between breccia and their special distribution, and stress analyzing the joint structures in and around the breccia pipe, it is found that the observed phenomena are caused by a new tectonic dynamic mechanics of fluid—double-fracturing caused by temperature and pressure of fluids and pulsating expansion. Under the actions of thermal stress and the pressure of fluids, thermal cracks and joints that developed along parts of the thermal cracks formed systematically in the rocks. Under these conditions, up-arching fracture zones that pulsatively expanded upward and cylindrical pressing breccia body were formed. Rocks at the peak of the pyramidal fractures zone break down instantly. Where the difference between pressure of fluids and the overburden pressure exceeded greatly the competence of the rocks, fluid junctions occurred and the velocity of the fluid flow increased as a result. Explosive body expanded upward in the shape of an inverse cone, cone-like explosive breccia body and cover-like shattering breccia body located on the upper part of the breccia pipe were ultimately formed. Gold-rich fluids were enriched and mineralized near the boiling surface in the lower part of the inverse cone-like explosive breccia body where temperature and pressure decreased rapidly, while copper-rich fluids were enriched and mineralized in the junction area where temperature and pressure were relatively high.

Explosive microfractures induced by K-metasomatism

Abstract Ultra-fine mineral aggregates in K-metasomatic rocks of the Hougou area, northwestern Hebei Province, China contain peculiar and distinct intergranular and intragranular geometries, compositions, and textures. These features indicate solidification of expanded and enclosed relict fluids within tensile microfractures. Two basic morphologic types of textures are present: saw-toothed and wheel-shaped, and several composite patterns also are present, such as X-shaped, grid, and network. The appearance of these features indicate explosion from an instantaneous force. These microscopic explosive microfractures are directly related to the enclosed relict fluids. Theoretical estimates show that volume expansion induced by mineral replacements during K-metasomatism may have caused the K-metasomatic fluids to be confined and strongly compressed in order to build up powerful forces that produced the ultra-fine mineral aggregates and explosive microfractures. The thick-walled texture of K-metasomatic rocks confined fractures that propagated only in the replaced rocks with the lowest strength. Both pumping pressures and the propagation of the K-metasomatism were self-governed and controlled by introduced chemical elements, specially K+.

Zhengguang: A potentially large, high-grade epithermal gold deposit in the Duobaoshan metallogenic belt, Heilongjiang, northeastern China

Traditional ideas and methods are of limited use in deep prospecting in plant and volcanic-covered areas in Heilongjiang Province. The application of the authors’ ‘three-field anomaly interrestrain’ theory and a new geological-geophysical-geochemical prospecting technique combination has helped the local geological team to learn more about ore-controlling structural and metallogenic information under the cover. Subsequent drilling programs have revealed and assessed a potential large high-grade epithermal gold deposit in the southeastern part of the important porphyry copper belt.