Potential Exploration Targets Research Articles

Factors Controlling Natural Gas Accumulation in the Southern Margin of Junggar Basin and Potential Exploration Targets

In this paper, factors controlling natural gas accumulation in the southern margin of Junggar Basin were mainly discussed by a comparison with natural gas generation and accumulation in the Kuqa Depression of Tarim Basin. The southern margin of Junggar Basin and the Kuqa Depression of Tarim Basin are located on the north and south sides of the Tianshan Mountains respectively, and they share the similar sedimentary stratigraphy and tectonic evolution history. In recent several decades, many large gas fields have been found in the Kuqa Depression of Tarim Basin, but no great breakthrough in the southern margin of Junggar Basin. Our results suggest that natural gas in the southern margin of Junggar Basin is mainly thermogenic wet gas, and can be divided into three types as coal-derived gas, mixed gas and oil-associated gas, of which the former two types are dominated. The Jurassic coal measures are the main source rocks of natural gas, and the main gas generation time from this set of source rocks matched well with the formation time of the anticline structures, resulting in favorable conditions for natural gas accumulation. In the western part of the southern margin in the Junggar Basin, the Permian lacustrine and the Upper Triassic lacustrine-swamp source rocks could be important sources of natural gas, and the main gas generation time also matched well with the formation time of traps. Compared with the Kuqa Depression of Tarim Basin, natural gas sources are better in the southern margin of Junggar Basin, and the geologic conditions are favorable for the formation of large oil and gas fields in the southern margin of Junggar Basin. The deep Permian-Jurassic-Cretaceous petroleum system is the most favorable petroleum system for natural gas exploration in the southern margin of Junggar Basin. The western part and the central part of the southern margin in the Junggar Basin could be the first targets for the discovery of the Jurassic coal-derived oil and gas reservoirs. The shallow Cretaceous-Neogene petroleum system is the second target for natural gas exploration.

Rift and salt-related multi-phase dolomitization: example from the northwestern Pyrenees

The Meillon (Callovo-Oxfordian) and Mano (Tithonian) Formations are dolomitized carbonate reservoirs that actively produce oil and gas (Aquitaine Basin, France). In this study, the dolomitization conditions of their counterparts exhumed in the northwestern Pyrenees are detailed using a combination of field observations, petrography, fluid inclusion microthermometry, elemental and isotopic geochemistry, and carbonate U–Pb geochronology. Dolomitization occurred in several stages spanning from the Neocomian (pre-rift) to the Albian (syn-rift, associated with mantle exhumation and active salt tectonics). Both formations were first massively dolomitized in near-surface to shallow burial conditions during the Berriasian-Valanginian, likely triggered by the influx of marine-derived waters. Between the Barremian and the Albian, the Early Cretaceous rifting caused the upward influx of hot fluids associated with the partial to complete recrystallization of the initial dolomites. During the Albian, subsequent dolomites precipitated in both formations as high-temperature (T > 160 °C) vein- and pore-filling cement. Distinct fluid inclusion chlorinities and rare earth element patterns between the Meillon and Mano Formations point to fluid compartmentalization during this stage. Whereas dolomite cements indicate the involvement of evaporite-derived brines in the Meillon Formation, precipitation was likely related to clay-derived water in the Mano Formation. Lastly, a final episode of dolomite cementation occurred only in the vicinity of faults and volcanic intrusions during the Albian when the highest temperatures were recorded in both formations (T > 250 °C). These saddle dolomites precipitated from hydrothermal water with a mixture of mantle-, crustal-, and evaporite-derived waters channeled by faults and active diapirs. Subsequent quartz and calcite cement precipitation reveals a temperature decrease in a post-rift to inversion setting (post-Cenomanian) and indicates fluid compartmentalization between both formations. This study highlights the major control exerted by rifting, combined with the presence of diapiric salt, on dolomitization, making carbonate platforms of modern salt-rich passive margins potential targets for exploration.

Identification of potential targets for kimberlite exploration using satellite imagery and map combination approach in the Lesotho Kimberlite Province

This study presents the use of satellite data and map combination approach for kimberlite exploration to identify follow-up exploration targets. The study area falls in the Lesotho Kimberlite Province, which hosts diamondiferous kimberlite pipes such as Letseng and Kao in Lesotho, and Monastery and Jagersfontein in South Africa. This study focusses on processing and integration of evidential map layers (geomorphic features, linear structures and kimberlite indicator minerals) that have known correlation with kimberlite occurrence. The evidential map layers were acquired from satellite platforms such as ASTER and SRTM DEM. These layers were integrated to identify favourable sites for detailed follow-up exploration by subdividing the area into high, moderate and low prospective regions based on the number of controlling evidences operating in each sub-region. A follow-up sampling and ground magnetic survey were carried out at one of the high prospective zones to validate the results of the present approach. Kimberlite indicator minerals such as garnet, diopside, ilmenite and chromite were recovered from the collected sample. Several garnets show adhering materials known as kelyphite rims, which are typical surface features of peridotitic garnets having close relationship with diamondiferous kimberlite. Keating correlation coefficient, which uses a simple pattern recognition to locate magnetic anomalies that resemble the response of modelled kimberlite pipes, was applied to ground magnetic data. We used a series of reference kimberlite models composed of homogeneous vertical cylinders of various radius ranging from 50 to 200 m and depth varying from 50 to 500 m. The correlation coefficients between analytical signal grid of modelled kimberlite pipe and observed magnetic data were computed. Following this approach, kimberlite model with correlation coefficients exceeding 80% was selected. By matching the response of modelled kimberlite pipe with the magnetic anomalies, four pipe-like targets were located. The target(s) may be a potential source of the recovered kimberlite indicator minerals since the morphology of these minerals suggest a proximal kimberlitic source.

Spatio-Geologically Informed Fuzzy Classification: An Innovative Method for Recognition of Mineralization-Related Patterns by Integration of Elemental, 3D Spatial, and Geological Information

Recognition and mapping of mineralization-related patterns in geochemical data is a key computational analysis to achieve a predictive model of prospectivity for mineral deposit occurrence. This contribution describes a spatio-geologically informed fuzzy classification (SGIFC) for portraying the spatial-frequency distribution of mineralization through integration of geochemical concentrations, 3D spatial properties, and geological knowledge contained in surface samples. A spatio-geological interaction model (SGIM) was defined to constitute an SGIFC by modulating fuzzy memberships in each iteration of standard fuzzy c-means (FCM) according to the incorporation of both spatial and geological inter-sample similarities. This strategy was adapted to the compositional nature of multi-elemental data and implemented by programming over packages supplied within the R language environment. A comparative experiment on soil samples collected in a porphyry Cu–Au system was subjected to understand how the SGIM affects standard memberships spatially, statistically, and geostatistically. Spatial autocorrelation analysis of fuzzy memberships through Moran’s I calculation and Monte Carlo simulation indicated that SGIFC leads to more robust spatially connected patterns compared to FCM models. Moreover, variogram analysis illustrated that SGIM orients the spatial continuity of mineralization-related memberships along the diffusion bearing of hydrothermal fluids across geological structures of the study area. Rock samples collected along trenches, as well as Cu volumetric productivities, were used as benchmarks to evaluate the integrity of the derived predictive models. The results reveal that the distribution pattern of mineralization-related memberships for SGIFC, compared to that of FCM, is more consistent with sub-outcropping and deep metallogenic realities and describes a more significant quantitative association with subsurface mineral content within the study region. The incorporation of SGIM into fuzzy classification has demonstrated the sufficiency to synthesize the comprehensive information of samples to predict effectively potential targets for follow-up exploration.

Inducing moral elevation in veterans with PTSD: An experimental investigation using a mixed methods approach

Moral elevation is a positive emotion described as feeling inspired by others’ virtuous actions. Elevation has several psychosocial benefits, some of which may be relevant to trauma-related distress; however, past studies have primarily examined elevation in nonclinical, civilian populations or in naturalistic studies. This experimental study used mixed methods to assess if veterans with post-traumatic stress disorder (PTSD) experience elevation when exposed to elevation stimuli in a controlled setting. Participants included 47 veterans with significant PTSD symptoms. Following baseline measures and a written trauma narrative, veterans were randomized to an elevation or amusement condition where they viewed two videos intended to elicit the condition emotion. Veterans also provided a written journal response describing their reaction to the videos. Self-report measures were administered after each study task to assess state-level elevation and amusement. Veterans randomized to the elevation condition reported significantly higher levels of elevation after videos compared to veterans in the amusement condition. Qualitative results offered further support for differences between groups and identified unique themes related to the experience of elevation. Overall, findings indicate it is possible to induce elevation in veterans with significant PTSD symptoms. Additionally, qualitative results highlight specific benefits of elevation and potential targets for treatment integration and future exploration.

Integrated reservoir characterization based on a comprehensive study of the geological structure using 3D seismic survey

The 3D seismic survey is the undisputed leader among tools of identifying potential exploration targets and reservoir characterization. This paper shows surveys that are crucial in the exploration and development of significant amounts of hydrocarbon resources, and enables operator companies to map complex geological structures and select better drilling locations. The purpose of the research is to have better understandings of formations and update previous studies in the oil field of Mangyshlak Basin, Western Kazakhstan. The Main results are the acoustic impedance, Vp/Vs ratio, lithological and reservoir properties data. The quality controls and analysis of results show a good match with well logs and good recovery of seismic signal in inversion, but it should be improved in some areas. The results, from a scientific point of view, expand the already known geological and geophysical studies of the reservoir and improve the quality of interpretation using seismic methods in studying the sedimentation environment.

Cumulate olivine: A novel host for heavy rare earth element mineralization

Abstract Olivine is one of the most important minerals used to reconstruct magmatic processes, yet the rare earth element (REE) systematics of Fe-rich olivine in igneous rocks and ore deposits is poorly understood. As detected by in situ laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analysis, cumulate fayalite (Fe2SiO4) in the Paleoproterozoic Vergenoeg F-Fe-REE deposit of the Bushveld large igneous province (LIP) in South Africa contains the highest heavy REE (HREE) contents ever recorded for olivine, with HREE enrichment of as much as 6000× chondritic values. Atom probe tomography maps confirm the incorporation of the HREEs into the fayalite crystal lattice, facilitated by lithium acting as a main charge balancer and by high REE contents in the highly fractionated felsic parental melt that is related to the Bushveld LIP. The high HREE concentrations of fayalite in concert with its high modal abundance (>95 vol%) indicate that the fayalite cumulates are the main host for the HREE mineralization of the Vergenoeg deposit. Fayalites of Vergenoeg demonstrate that Fe-rich olivine may fractionate large amounts of HREEs, and we propose fayalite cumulates as potential future targets for HREE exploration.

Integrative analysis of hepatic metabolomic and transcriptomic data reveals potential mechanism of nonalcoholic steatohepatitis in high-fat diet-fed mice.

Due to the complex pathogenesis, the molecular mechanism of nonalcoholic steatohepatitis (NASH) remains unclear. In this study, we aimed to reveal the comprehensive metabolic and signaling pathways in the occurrence of NASH. C57BL/6 mice were treated with high-fat diet for 4 months to mimic the NASH phenotype. After the treatment, the physiochemical parameters were evaluated, and the liver tissues were prepared for untargeted metabolomic analysis with ultraperformance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry. Then, three relevant Gene Expression Omnibus (GEO) datasets were selected for integrative analysis of differentiated messenger RNA and metabolites. The levels of phosphatidylethanolamine (PE) (16:1(9Z)/20:4(5Z,8Z,11Z,14Z)), oleic acid, and sphingomyelin (SM) (d18:0/12:0) were significantly increased, and the content of adenosine was severely reduced in NASH mice. The integrated interpretation of transcriptomic and metabolomic data indicated that the glycerophospholipid metabolism and necroptosis signaling were evidently affected in the development of NASH. The high level of SM (d18:0/12:0) may be related to the expression of acid sphingomyelinase (ASMase), and the elevated arachidonic acid was coordinated with the upregulation of cytosol phospholipase A2 (cPLA2) in the necroptosis pathway. In summary, the inflammatory response, necroptosis, and glycerophospholipid may serve as potential targets for mechanistic exploration and clinical practice in the treatment of NASH.

Mesogenetic diagenesis of the Ordovician limestone in Yubei area, Tarim Basin, NW China

The Lower Ordovician succession, consisting of the Yingshan and Penglaiba formations, encompasses significant petroleum reservoirs in Yubei area, southwest Tarim Basin. Mesogenetic dissolution and dolomitization strongly contributed to the increase in rock porosities here. Wells YB 7, YB 5, and YB 1-2X drilled in eastern Yubei area met the deposits of Yingshan and Penglaiba formations, providing abundant data for the mesogenetic diagenesis analysis. Among them, Well YB 5 encountered the thickest Penglaiba Formation and was chosen for detailed analysis. Eight diagenetic elements (i.e., micrite encrust, radial fibrous calcite cement, stylolites, poikilotopic calcite cement, dolomite, fracture, bladed quartz, and equant quartz) are identified and ascribed to seven paragenetic events. Their Paragenetic sequence evidences Yingshan and Penglaiba Formations experienced severe deep burial diagenesis. The presence of green luminescent fluorite, non-luminescent and zoned quartz, and violet to orange luminescent saddle dolomite with sweeping extinctions, together with the positive Eu2+ anomalies shown in the rare earth element (REE) patterns all help to ascribe the buried dissolution and dolomitization to the incorporation of hydrothermal fluids. The inconsistency between the REE patterns of the Yingshan and Penglaiba formations and that of the organic-rich source rocks of Lianglitage and Bachu Formations exclude the assumption that hydrocarbon influx caused the mesogenetic dissolution. High-angle fractures, generated by the Middle Caledonian–Early Hercynian tectonic movements, acted as conduits for hydrothermal fluid migration and promoted the mesogenetic dissolution to form dolomite reservoirs. The coincidence that samples with positive Eu2+ anomalies all fall in the basalt province, while samples lacking positive Eu2+ anomalies from Tahe fall out, backs up that the main source of the hydrothermal fluid promoting the mesogenetic dissolution was probably derived from the Permian magma. Strata possessing similar geochemical and petrological characteristics as Yingshan and Penglaiba formations in eastern Yubei area, and experiencing subsequent tectonic and magmatic activities could be potential exploration targets in further exploration practice in Tarim Basin and in the other basins in the world.

Proteome Responses to Individual Pathogens and Abiotic Conditions in Rice Seedlings.

Rice plants under field conditions experience various biotic and abiotic stresses and are adapted to survive using a molecular cross-talk of genes and their protein products based on the severity of a given stress. Seedlings of cultivated variety ASD16 (resistant to fungal disease, blast; tolerant to abiotic stress, salinity) were subjected to salt, drought, high temperature and low temperature stress as well as infection by Rhizoctonia solani and Xanthomonas oryzae pv. oryzae (causing reemerging diseases such as sheath blight and leaf blight), respectively, the sheath blight and bacterial leaf blight pathogens. Leaf proteome was analyzed using two-dimensional electrophoresis and differentially expressed proteins were identified using mass spectrometry. In addition to many other differentially expressed proteins, acidic endochitinase was found to be upregulated during fungal infection and drought treatment, and a germin-like protein upregulated during fungal infection and high temperature stress. These two proteins were further validated at the gene expression level using reverse transcription-PCR in dual stress experiments. Pot culture plants were subjected to fungal infection followed by drought and drought followed by fungal infection to validate chitinase gene expression. Similarly, plants subjected to fungal infections followed by high temperature stress and vice versa were used to validate the expression of germin-like protein-coding gene. The results of the present study indicate that chitinase and germin-like protein are potential targets for further exploration to develop rice plants resistant or tolerant to biotic and abiotic stresses.

APPLICATION OF SEISMIC METHODS FOR INTEGRATED RESERVOIR CHARACTERIZATION

3D seismic survey is the undisputed leader among tools of identifying potential exploration targets and reservoir characterization. This paper shows surveys that are crucial in the exploration and development of significant amounts of hydrocarbon resources, and can be used by operator companies to map complex geological structures and select better drilling locations. The purpose of research work is to have better understandings of formations and update previous studies in oil field of Mangyshlak Basin, Western Kazakhstan. The Main resultsare the acoustic impedance, Vp / Vs ratio, lithological and reservoir properties data. The quality *Автор для переписки. E-mail: zhak28@gmail.com НЕФТЬ И ГАЗ 2020. 3–4 (117–118) 85 ГЕОФИЗИКА controls and analysis of results show good match with well logs and good recovery of seismic signal in inversion, but it should be improved in some areas. The results, from a scientific point of view, expand the already known geological and geophysical studies of the reservoir and improve the quality of interpretation using seismic methods in studying the sedimentation environment of the site.

Sedimentary characteristics and exploration direction in the south of the central block in Pre-Caspian Basin

The Pre-Caspian Basin experienced the history from the Late Paleozoic craton margin to the Mesozoic-Cenozoic depression. It has been explored for a long time. It is the most important oil and gas producing area in Kazakhstan, and a large number of oil and gas fields have been discovered in it. The oil and gas discoveries are located in clastic rock and platform carbonate rock below the Lower Permian salt domes. The study area is located at the eastern margin of the Pre-Caspian Basin, where reservoirs are deposited in an open carbonate platform in the shallow sea. The most developed subfacies are intraplatform shoals and sea between shoals. The microfacies in the intraplatform shoals include bioclastic shoals and algae shoals, and represent dominant high-quality reservoirs. The central gentle zone and the eastern slope zone in the study area are potential targets for exploration and evaluation. All reservoirs are structural-lithologic reservoirs controlled by high lithologic barriers or updipped pinch-outs.

Evaluation of hydrocarbon potential using fuzzy AHP-based grey relational analysis: a case study in the Laoshan Uplift, South Yellow Sea, China

Abstract Effective evaluations of hydrocarbon potential contribute to delineating promising target areas for further exploration. Sparse available data and known hydrocarbon reservoirs in frontier areas present considerable challenges to the weighting of geological factors when evaluating hydrocarbon potential. This study proposes a hydrocarbon potential mapping method that employs grey relational analysis (GRA) based on a fuzzy analytic hierarchy process (fuzzy AHP). GRA is a comprehensive evaluation method that represents the hydrocarbon favourability according to the proximity between evaluation targets and the ideal target based on multiple evaluation factors and weights among them. To overcome the uncertainty and vagueness in the weighting procedure, the fuzzy AHP technique relies on experts’ knowledge to define the relative importance of evaluation factors and exploits triangular fuzzy numbers to simulate experts’ judgements in pairwise comparisons. The fuzzy AHP-based GRA method was tested using an example in the Laoshan Uplift in the South Yellow Basin of China. This test application not only quantified the favourability of local traps but also revealed their spatial variations on favourability maps and indicated potential targets for further exploration. The results obtained by the fuzzy AHP-based GRA method were more reliable than that of entropy weight-based GRA and displayed a suitable consistency with known geological information, thus demonstrating that such a procedure could reveal the potential spatial features of hydrocarbon accumulations and support the evaluation of hydrocarbon potential in relatively unknown areas.

Hypozonal orogenic gold mineralization in the Giyani Goldfield, Northern Kaapvaal Craton/Limpopo Complex

Abstract The paper reviews published and unpublished geological data pertaining to the structural and metamorphic controls, rock types, characteristic features, source, and timing of hypozonal orogenic gold mineralization in the Giyani Goldfield. The Giyani Goldfield includes the NW domain of the >3.0 Ga Giyani greenstone belt (GGB) at the northern edge of the Kaapvaal Craton and the southern retrograde hydrated domain of the juxtaposed Southern Marginal Zone (SMZ) of the ca. 2.72 Ga Limpopo Complex (LC). Mineralization at all gold mines and gold prospects of the Giyani Goldfield is structurally controlled and closely associated with the Hout River shear zone (HRSZ) and associated smaller shear zones suggesting a specific tectonic setting. This tectonic setting is the direct consequence of thrusting the SMZ of the LC against and over the adjacent GGB at the position of the steeply north-dipping (south verging) HRSZ during the exhumation stage of the ca. 2.72 to 2.69 Ga Limpopo orogeny followed by regional retrograde hydration of the southern part of the SMZ at ca. 2.68 to 2.62 Ga. This tectonic setting offers an explanation for a deep-seated crustal source for gold and for the concentration of orogenic gold mineralization within specific structural features located within the Giyani Goldfield. This tectonic setting also explains the lithological, structural and metamorphic complexity, metasomatic alteration and post-peak metamorphic timing of gold mineralization. Finally, it provides important clues with regards to a crustal source for gold mineralizing fluids and the identification of new potential targets for gold exploration in the Giyani Goldfield.

Reflection waveform inversion based on full-band seismic data reconstruction for salt structure inversion

SUMMARYSalt structures are high potential targets for oil and gas exploration. However, large-scale salt domes with irregular surfaces pose significant challenges for velocity model building. For full waveform inversion, in the absence of a high-fidelity initial model, the success of the inversion depends on low-frequency seismic data, which are scarce in the exploration data sets. This paper presents a new idea to solve the problem of salt structure velocity modelling. First, we propose an envelope-based full-band seismic data reconstruction algorithm. The smoothness of envelope is used to segment the events in seismic data, and the phase independence of envelope is used for the identification of the seismic event's arrival-time to obtain the apparent reflection sequences of the subsurface. Full-band seismic data are obtained by convolving the apparent reflection sequence with full-band source. Window averaging function and threshold strategy are used to ensure the accuracy of seismic event segmentation and the stability of the algorithm when dealing with noisy data. Then the multiscale reflection waveform inversion based on reconstructed data is proposed for salt structure velocity building. The numerical experiment results of the Sigbee2A model demonstrate the performance of the inversion algorithm in the case where the seismic data lack low-frequency components and contain noise. The limitations of the algorithm have also been analysed and studied.

Metallogenic model of the Wulong gold district, China, and associated assessment of exploration criteria based on multi-scale geoscience datasets

The combined use of geological and geophysical modeling is effective for delineating subsurface exploration criteria and conducting quantitative analyses to determine potential mineral targets. In this paper, total horizontal derivative, multi-scale edge detection (worms), and bi-dimensional empirical mode decomposition (BEMD) of district-scale gravity and magnetic data were applied to extract geophysical information reflecting deep-seated structures and concealed intrusions. In addition, deposit-scale 3D modeling and controlled-source audio-frequency magnetotelluric data were used to identify potential ore-controlling structures. The results of our integrated multi-scale geological and geophysical studies suggest that the Early Cretaceous intrusions and gold deposits in the Wulong gold district, which is located on the Liaodong Peninsula, China, at the NE margin of the North China Craton (NCC), are spatially and genetically associated with a network of NE- and NW- striking faults. Gravity and magnetic modeling effectively identified buried Early Cretaceous intrusions and NW- striking faults at depths from zero to five kilometers. In summary, the combined use of multiple-source and multi-scale geophysical information and multi-scale 3D geological modeling facilitated delineation of the metallogenic model and provided exploration criteria for determining potential exploration targets in the study area.

Reconstruction of sediment-dispersal patterns using seismic sedimentology in the southeastern Zhanhua Sag, Bohai Bay Basin, China

Reconstruction of sediment-dispersal patterns not only provides insight into paleogeographic evolution, but also sheds light on facies and reservoir prediction. By integrating core, wireline logs, and 3D seismic data, seismic sedimentologists have discovered several advantages to sediment-dispersal reconstruction and paleogeographic-environment analysis. We have subdivided the third member of the Shahejie Formation (Es3) of the southeastern Zhanhua Sag (Sanhecun Block) into three third-order sequences, namely SQ1, SQ2, and SQ3 from bottom to top. The facies architecture was analyzed by using the seismic sedimentology approach based on 3-D seismic data. Seismic RMS-amplitude stratal slices reveal different characteristics of the lobes among the southwest gentle slope, southern slope-break belt and north fault-controlled slope from source to sink. On the basis of an integrated analysis of well log, core data, seismic facies based on RMS attributes, three depositional environments (e.g., “fan-delta”, “turbidite” and “lacustrine” facies) have been recognized. Seismic RMS-amplitude stratal slices indicate that the depositional environments of these sequences evolved from medium-sized gravel-rich fan-delta and turbidite-fan deposits to small-scale mud-rich fan-delta deposits, and lastly to large-scale sand-rich fan-delta deposits. The changes of relative lake level and sediment supply rate control the lithology and size of different depositional systems. This study also suggests that the temporal and spatial evolution and distribution of depositional systems are influenced significantly by paleotopography and slope break in the systems tracts of different sequences of the Es3 in the southeast Zhanhua Sag, Bohai Bay Basin. In addition, fan-delta-front deposits could also be considered as future potential exploration targets because they are relatively sand- or gravel-rich, given the reconstruction of the sediment-dispersal pattern.

Geology of the Gouap iron deposit, Congo craton, southern Cameroon: Implications for iron ore exploration

The Ntem Complex represents the northwestern edge of the Archean Congo craton in southern Cameroon where numerous banded iron formation (BIF)-hosted iron deposits have been discovered. The Gouap iron deposit, which is located on the western edge of the Ntem Complex, is one of the recent discoveries of iron deposits in this area. In this study, geological mapping, detailed drillcore logging and petrographical studies reveal that the Gouap iron deposit comprises of two lithostratigraphic units, namely the BIF and the Country rocks. The BIF unit consists of amphibole BIF and amphibole-pyrite BIF, whereas the Country rocks unit is made up of gneisses (garnet, amphibole–magnetite and amphibole–garnet–pyrite gneiss), schists (amphibole–magnetite and garnet–magnetite micaschist), quartzites and dolerite sills.The BIFs are well interlayered and observed to be in sharp or gradational contacts to their associated country rocks. The mineral assemblages of the BIFs and wallrocks (except the dolerites) indicate that both units have been metamorphosed under amphibole facies conditions. Two main iron mineralization types are identified in the Gouap deposit: the soft iron type which is mainly located in the western and northern parts and the hard iron type mostly confined to the southern sector of the deposit.The structural controls of the Gouap iron deposit are better observed in drillcore samples other than on the outcrop-scale. There are three principal deformation events (D1, D2 and D3) that led to the development of foliation, folding and faulting respectively. The iron mineralization are mostly concentrated on the F2 fold hinge zones and fractures that acted as passage ways for the circulation of meteoric water at surface. We suggest that the following three major processes that led to the formation of the Gouap deposit: (i) the chemical precipitation of chert and iron-oxide followed by sedimentation and diagenesis that formed chert–magnetite BIFs; (ii) secondly, the amphibolite facies metamorphism and deformation that formed quartz–magnetite BIFs, which constitute the main iron ridge located on thicker zones of fold noses; and (iii) finally, the Gouap BIFs have been upgraded to medium-grade iron ore due to supergene enrichment processes, which are restricted to the modern land surface and locally reached deeper levels through fault and fracture zones. The western and northern parts of the Gouap deposit have been identified as potential exploration target areas for iron mineralization. Even though the iron formation processes of the Gouap deposit are not yet completely understood and many questions remain unanswered regarding the genesis of the soft and hard iron mineralization, these new insights have important implications on the exploration drilling strategies of this deposit.

Automated Identification of Magnetic Responses from Porphyry Systems

Porphyry-style mineralisation often appears as near circular anomalies within magnetic data. This article presents an automatic grid analysis system to detect such responses. Our approach follows three steps: (1) Find circular features using the radial symmetry transform; (2) Validate the detected features by the presence of high magnetic contrast at the feature location; and (3) Highlight the alteration zone boundary using deformable splines. The outcome of this system is two-fold. First, provide estimates of the location of potential porphyry systems, and second, accentuate the appearance of potential exploration targets to aid manual data inspection. Experiments were conducted on survey data from Reko Diq, Pakistan, a region known to contain numerous occurrences of porphyry-style mineralisation. The prediction results of our system closely matched the location of the known deposits in this region thus rendering confidence in the effectiveness of our approach. It is suggested that this system be used as an initial screening tool for large datasets, therefore reducing the time and cost imposed by manual data inspection in the exploration targeting process.

Hydrocarbon migration and accumulation in the northwestern Bozhong subbasin, Bohai Bay Basin, China

An important exploration breakthrough has been achieved in the western subsag of the Bozhong subbasin, but the hydrocarbon accumulation mechanism was not clear. The hydrocarbon migration and accumulation mechanism of the western subsag of the Bozhong subbasin is discussed based on the modeling of hydrocarbon migration pathways and the study of late-stage reactivation of neotectonic faults. Three processes for lateral petroleum migration and accumulation can be recognized in the studied area: 1) migration and accumulation along the T8 unconformity; 2) migration and accumulation within the Guantao Formaiton (N1g); and 3) interaction of migration and accumulation along the T8 unconformity and Guantao Formation (N1g). The reactivation of faults in the studied area began 5.1 Ma. Following hydrocarbon lateral migration, late-stage reactivated neotectonic faults serve as effective vertical conduits for hydrocarbon migration and accumulation into the shallow Minghuazhen Formation (N1m) reservoirs.The modeling results of preferential petroleum migration pathways (PPMPs) and favorable accumulation areas are consistent with the actual exploration results. Two kinds of potential exploration targets can be predicted in the northwestern Bozhong subbasin: the first kind is hydrocarbon accumulation areas near or within generative kitchens (e.g. Target 1); the other kind is hydrocarbon accumulation areas removed from the generative kitchens, but with hydrocarbon sourcing from multiple generative kitchen and numerous PPMPs (e.g. Target 2). Studying preferential petroleum migration pathways will help reduce exploration risk.