Rotation of the Semail ophiolite (Oman): Additional Paleomagnetic data from the volcanic sequence

Thirty-two flows (247 cores) were sampled in the V1 (Geotimes) and V2 (Lasail) volcanic units of the Semail ophiolite, Oman (Aswad, Fizh, Hilti, Sarami, Wuqbah, and Tayin massifs). Paleomagnetic analysis of the samples was complicated by a large overlap of the two components of magnetization carried by the rocks: a crystalline remanent magnetization (CRM) acquired in the present day field, probably during weathering, and an older CRM probably produced by oxidation of the original titanomagnetites during hydrothermal event(s). If the magnetization carried by the V1 samples was acquired during the hydrothermal event related to the emplacement of these lava, e.g., during and/or shortly after cooling, the tectonic unity of the northern domain has to be questioned and a differential rotation considered between the Aswad and Hilti-Sarami massifs but, by the time of emplacement of the V2 series, this northern area seems to behave as one large unit. As only one set of data is available for the southern Tayin-Sumail massif, it is premature but a possible relative rotation on the order of 90° can be suspected between the Hilti-Sarami and Tayin-Sumail massifs, rotation which would have occurred after emplacement of the V2 series.     

Synthetic hydrograph generation by hydrological donors

A method to build synthetic hydrographs is introduced, based on 1300 gauging stations in France and Switzerland, covering a wide range of size and climatology. For each station, an average of two floods per year are selected by a peak-over-threshold method, providing about 69?000 hydrographs. For a given catchment, some “donor stations” are selected with criteria of proximity in space, size and runoff production. These donors provide hundreds of hydrographs which can complement the ones recorded locally, or replace them if no hydrograph is available. With this subset of hydrographs, one can estimate the catchment’s average peak-to-volume ratio of floods, and build the corresponding median hydrograph. Another application is, for a given daily discharge sequence (being observed or simulated), to generate a relevant synthetic hydrograph by combining appropriate hydrographs of the subset. These methods are assessed by performing a jack-knife validation on a wide dataset of stations.     

Analytical model for the in‐plane seismic performance of cold‐formed steel‐framed gypsum partition walls

This paper proposes an experimentally verified procedure to analytically model cold‐formed steel‐framed gypsum nonstructural partition walls considering all the critical components. In this model, the nonlinear behaviors of the connections are represented by hysteretic load‐deformation springs, which have been calibrated using the component‐level experimental data. The studs and tracks are modeled adopting beam elements with their section properties accounting for nonlinear behavior. The gypsum boards are simulated by linear four‐node shell elements. The proposed procedure is implemented to generate the analytical models of three full‐scale partition wall specimens in the OpenSees platform. The specimens were tested as a part of the NEESR‐GC Project on Simulation of the Seismic Performance of Nonstructural Systems. Force‐displacement responses, cumulative dissipated energy, and damage mechanisms from the analytical simulation are compared to the experimental results. The comparison shows that the analytical model accurately predicts the trend of the response as well as the possible damage mechanisms. The procedure proposed here can be adopted in future studies by researchers and also engineers to assess the seismic performance of partition walls with various dimensions and construction details, especially where test data are not available. Copyright © 2015 John Wiley & Sons, Ltd.     

Mineral Resources: The Bread and Butter of NRR

Natural Resources Research -     

Multi-scale Numerical Simulation and 3D Modeling for Deep Mineral Exploration in the Jiaojia Gold District,China

In this study, deposit- and district-scale three-dimensional (3D) fault-and-intrusion structure models were constructed, based on which a numerical simulation was implemented in the Jiaojia gold district, China. The numerical simulation of the models shows the basic metallogenic path and trap of the gold deposits using mineral system theory. The objective of this study was to delineate the uncertainty of the geometry or buffer zones of the ore-forming and ore-controlling fault-and-intrusion domains in 3D environment representing the exploration criteria extraction and the gold potential targeting in the study area. The fast Lagrangian analysis of continua in three dimensions was used as the platform to define the stress deformation fracture ore storage and the hydrothermal seepage channel zone based on the gold deposit features and metallogenic model in the study area. The validity of the numerical simulation was verified by comparing it with robust 3D geological models of the large Xincheng gold deposit. The potential targeting zones are analyzed for uncertainty and then evaluated by Boolean operation in a 3D geological model using the computer-aided design platform. The research results are summarized as follows. (1) In the pre-mineralization period, the Jiaodong fault’s left lateral movement created the Jiaojia network faults and formed a fracture zone with NW- to NNW-trending dips of 20° to 40°. (2) During the mineralization period, hydrothermal flow was associated with the intrusion geometry and features. However, it was constrained by the Jiaojia fault, which blocked the vadose flow into the upper wall rock and made the hydrothermal route close to the fault in the footwall fracture zones. (3) Three gold potential targets were identified by the numerical simulation results in the study area: the NW-trending Sizhuang gold deposit, the NW-trending zone of Jiaojia gold deposit, and the NE-trending zone of the Xincheng gold deposit. (4) The numerical simulation results show the fault-and-intrusion metallogenic domain and the hydrothermal alteration zones, which reflect the main ore-controlling and ore-forming factors of mineralization. The information obtained through the numerical simulation discussed here can be used to define exploration criteria in the study area.

     

Characterization of Secondary Native Selenium in the Yutangba Se Deposit,Western Hubei,China

Secondary native Se minerals that are appreciably coarser grained and vary morphologically than primary native Se minerals were observed in the abandoned dumps of the No. 3 and No. 4 orebodies of the Yutangba Se deposit, western Hubei Province, China. The secondary native Se minerals exhibit three crystal forms, namely prismatic, tabular, and granular. Based on geochemical and mineralogical data, the secondary native Se minerals are interpreted to have resulted from natural oxidation of selenide minerals in the primary Se ores, or from vaporization of Se caused by burning of “stone coal” (a highly carbonaceous mudstone) during the production of lime. The occurrence of secondary native Se minerals in the deposit would be helpful not only to further study on mineralogy, ore geochemistry and environmental geochemistry of Se, but also to improve the technology of reclaiming Se from the black rock series.     

U–Pb Ages for Zircon Grains from Nsanaragati Alluvial Gem Placers: Its Correlation to the Source Rocks

The Mamfe Basin is located in the SW of Cameroon and is an extension of the much bigger Benue Trough in the SE of Nigeria. Along the Asenem River and its tributaries in the western part of the Mamfe Basin (close to the border with Nigeria) gem placers yielding big zircon grains were found in recent river sediments close to Nsanaragati. In order to determine the source area and to establish a possible correlation between the zircons found in the Nsanaragati placers and rocks surrounding the Mamfe Basin 56 detrital zircon grains were analysed regarding their U–Pb ages and selected trace element contents by LA‐ICP–MS techniques. Possible source areas are rocks from the Benue Trough in the West and from the Cameroon Volcanic Line (CVL) in the SE of the study area. Based on microscopic analyses it was possible to distinguish two groups of zircons: reddish and non‐reddish ones, where the latter group comprises color variations from brown to orange, yellow to even colorless. In general, the detrital zircons show high hafnium values (4576 to 12565 ppm) and very variable thorium (7.8 to 1565 ppm) and uranium values (13.4 to 687 ppm). The Th/U ratios vary from 0.4 to 2.3, allowing correlations for some zircon grains to kimberlitic, granitic or syenitic affinities. It was also possible to distinguish zircon grains crystallised in mafic mantle‐derived melts from those crystallised in felsic melts, e.g. from continental rift‐related magmatic systems. In general, the U–Pb zircon ages obtained range from 11.7 to 1949 Ma. All zircons of the reddish group yielded almost similar ages resulting in a Concordia age of 12.4 Ma (Serravallian), an age unknown from the Mamfe Basin so far. The group of non‐reddish zircons showed various ages ranging from Serravallian to Orosirian. It was possible to correlate the youngest ages with rocks known from intrusions along the CVL, dated with K/Ar or Ar/Ar methods. The most probable sources were Mount Bamenda and Mount Bambouto in the east of the Mamfe Basin. Cretaceous ages are interpreted as re‐recycled clastic sediments whose original source had been rocks in the south and the north of the Benue Trough and who had been eroded and deposited within the catchment area of the Asenem river system in the Mamfe Basin in post‐Cretaceous times. The oldest ages are assumed to represent the pan‐African and pre‐pan‐African basement of the Mamfe basin.     

Untapped Economic Resource Potential of the Neoproterozoic to Early Paleozoic Volta Basin,Ghana: A Review

Natural Resources Research - The ~?115,000 km2 Volta Basin of Ghana is one of the most studied geological terrains. However, unlike the Birimian and Tarkwaian which have been...     

Two Sides of the Same Coin: Formal and Informal Institutional Synergy in a Case Study of Wildlife Governance in Ghana

Abstract

There has been the call to forge a synergistic relationship between local ecological knowledge and formal institutions in the governance of natural resources. How do informal institutions complement the efforts of formal state regulation of natural resources? How does this complementation foster a regularized human–wildlife interaction? Adopting an ethnographic design, this study assesses the role of institutional complementation in natural resource governance using the case of Boabeng–Fiema Monkey Sanctuary (BFMS) in Ghana, West Africa. We purposively selected 33 informants relevant to the BFMS governance process. The study observes that the synergy between formal and informal institutions strengthens wildlife protection in BFMS and the surrounding villages. The usefulness of informal rules is enhanced if appropriately complemented with a formal institutional arrangement. Over time, it becomes necessary for informal rules to grow in dynamism to depict the principles of collaboration, inclusivity, and benefit arrangements.     

The effects of vegetative ash on infiltration capacity, sediment transport, and the generation of progressively bulked debris flows

Through the alteration of the physical characteristics of a landscape, such as the destruction of vegetation and the formation of a hydrophobic layer, a fire can dramatically amplify erosion rates. On the basis of field observations, it has been proposed that the deposition of a layer of ash on the ground surface can enhance the erosion of mountainous terrain by surface runoff and might even be a necessary condition for the generation of progressively bulked debris flows. In this study, a flume was constructed to investigate the role of ash in increasing both the volume and the transport capacity of runoff. The experiments demonstrated that the presence of ash on the soil surface reduces the ability of flowing water to infiltrate; this effect is even greater when the ash has been pre-wetted. In addition, the ability of ash slurries to infiltrate decreases with increasing ash concentration. The results also indicate that the transport capacity of runoff is enhanced by the incorporation of ash into the flow because of the increased fluid density. However, the addition of ash reduces the boundary Reynolds number such that, at high ash concentrations and with fine-grained sediment, sediment transport declines as the flow becomes hydraulically smooth. The experimental results were also used to evaluate the ability of steep flow fronts, a common characteristic of debris flows and flash floods, to increase sediment transport rates. Finally, it is proposed that ash slurries may evolve into progressively bulked debris flows through a positive feedback between fluid density, transport capacity, and erosivity.