Seismic imaging of Caosiyao giant porphyry molybdenum deposit using ambient noise tomography

As a new emerging seismic method for delineating subsurface structure, the potential of ambient noise tomography is investigated for mineral deposit targeting at exploration scale. This passive seismic technique was used to image the subsurface 3-D shear-wave velocity of the Caosiyao porphyry molybdenum (Mo) deposit in the North China Craton. Intriguingly, the key structures of this giant porphyry mineral system down to the depth of 2 km are characterized by distinct shear-wave velocity anomalies, with ore deposition sites and fluid pathways (faults) characterized by distinct velocity lows, while fluid drivers (granites) generate velocity highs. The 3-D shear-wave velocity anomalies, along with seismic reflection profile and potential field data, allow us to delineate the deep-seated ore-controlling structures including fault systems, granitic plutons and even ore deposition sites under thickly covered sediments in the study area. The results suggest that the occurrence of the Caosiyao ore deposit is closely related to the huge amount of magma fluid intruding along the channel of Datong-Shangyi fault at a depth of gt;2 km. Our study demonstrates that the ambient noise tomography technique has the accuracy and resolution needed for mineral exploration targeting at deposit scale, with a relatively lower environmental impact as well as lower cost than active-source seismology.

Newer results of Monte Carlo inversion of IP data in water base protection and ore exploration

The paper presents the latest results of Monte Carlo inversion of IP data in the areas of water base protection and ore exploration. The method of determining the time constant spectrum using Monte Carlo inversion and the parameters characterizing the degree of environmental contaminations and ore deposition are presented. Among the field applications in Hungary, the investigation of the ionic pollution of the Ráckeve water base and the characterization of the Felsőtelekes waste dump of the Rudabánya iron ore mine are presented. In addition to these, the paper presents the investigation of ore deposition in the area of a gold mine in Mongolia using the Monte Carlo inversion of multi-electrode pole-dipole IP method.

Graphite from Palaeoproterozoic enhanced carbon burial, and its metallogenic legacy

The episode of widespread organic carbon deposition marked by peak black shale sedimentation during the Palaeoproterozoic is also reflected in exceptionally abundant graphite deposits of this age. Worldwide anoxic/euxinic sediments were preserved as a deep crustal reservoir of both organic carbon, and sulphur in accompanying pyrite, both commonly >1 wt %. The carbon- and sulphur-rich Palaeoproterozoic crust interacted with mafic magma to cause Ni–Co–Cu–PGE mineralization over the next billion years, and much uranium currently produced is from Mesoproterozoic deposits nucleated upon older Palaeoproterozoic graphite. Palaeoproterozoic carbon deposition has thus left a unique legacy of both graphite deposits and long-term ore deposition.

Post-Ore Processes of Uranium Migration in the Sandstone-Hosted Type Deposits: 234U/238U, 238U/235U and U–Pb Systematics of Ores of the Namaru Deposit, Vitim District, Northern Transbaikalia

To assess the nature of the post-ore behaviour of uranium in the Namaru deposit (Khiagda ore field), U–Pb isotope systems and the isotopic composition of uranium (234U/238U and 238U/235U) were studied. The studied samples represent different ore zones of the deposit and were collected along cross-sections both vertically and horizontally. Wide variations in the isotopic composition of uranium and U–Pb isotopic age have been established. Deviations of the 234U/238U ratio from equilibrium values, which for some samples exceed 50%, along with significant variations in the isotopic age, indicate that permafrost layer, which covered the catchment areas of paleovalleys with meteoric oxygen-containing waters ca. 2.5 Ma ago, did not lead to preserving uranium ores at the deposit. Uranium migration took place during the Quaternary period. The effective combining the U–Pb dating and 234U/238U data in assessing the post-ore redistribution of uranium made it possible to recognize: removal of uranium from some zones of the ore body and its accompanying redeposition in others. Wide variations in the 238U/235U (137.484–137.851) ratios throughout the entire studied cross-sections can be explained by the different locations of samples relatively to the ore deposition front and change in redox conditions as this front advanced. Depletion of the light isotope 235U in the lower zone of the ore body may be associated with the influence of ascending carbonic waters established in the regional basement. The effect of such waters on uranium-bearing rocks causes predominant leaching of light 235U.

Horizontal and vertical fluid flows as a key control of ore deposition at the basement/cover unconformity: insight from drone imagery of the Vendée coast, France

<p>Basement/cover interfaces are important transfer zones for hydrothermal fluids responsible for ore deposition, such as U and Pb-Zn deposits. Unconformities are peculiarly mixing zone where basement-derived fluids encounter sedimentary- and/or meteoric-derived fluids; leading to precipitation of these ores. Fluids are channelized by permeability contrast, i.e. impermeable barriers, until being trapped in porous units, i.e. intrinsic porosity and/or secondary porosity (dissolution and karstification process). In this configuration fracturing channelize the fluid flow by breaking impermeable barriers allowing external fluids to enter and react with the rocks (precipitation and/or dissolution). In this way, structural studies are crucial to highlight the fracture network and the potential of geological units to be good reservoirs.</p><p>In France, many occurrences of sediment-hosted deposits are known in Mesozoic basins (i.e. Aquitaine and Paris Basin) especially above the Variscan basement (Morvan district, SW Massif Central district, Poitou High district). The Vendée coast deposit (South Armorican Massif, France) is known for two Pb-Zn(-Ag) occurrences located in Liassic sediments overlying the Variscan basement. Previous works show that, during the Upper Jurassic extensional event (NNE-SSW horizontal stretching), the ore deposition results from the mixing of two different fluids: (1) low temperature brines following a horizontal path from evaporite to basin borders within Liassic sediments along the unconformity, (2) a high temperature and low salinity fluid rising up through the basement from several kilometres depth by a probable vertical pathway.</p><p>However, the permeability architecture leading to such mixing remains poorly constrained. The Vendée ore deposits present favourable outcrop conditions to study the structural control of the fluid plumbing system along the basement/cover unconformity. Structural studies assisted by drone imagery coupled with the characterization of the alteration-mineralization pattern show that:</p><p>(1) Horizontal path for basin brines is controlled by the impermeable barrier of the Toarcien layer overlying Liassic hosting karsts.</p><p>(2) Vertical path of basement-derived fluids is enhanced by new faults and inherited fractures, respectively generated and reopened by the Jurassic extension.</p><p>(3) Relative abundance of faults and veins in the Liassic sedimentary cover and the basement is consistent with a mechanical decoupling in a context of fluid overpressure.</p>