Petrophysics-guided velocity analysis and seismic data reprocessing to improve mineral exploration targeting in the Irish Zn-Pb Orefield

Introduction The Central Alborz in eastern Mazandaran province is host to the most important carbonate-hosted fluorite deposits in Iran, such as Pachi-Miana, Sheshroodbar, Era and Kamarposht. In these deposits, mineralization occurs in the upper parts of the middle Triassic Elika formation (Vahabzadeh et al., 2009 and references therein). These deposits have long been studied, and various models are presented for ore genesis. Nevertheless, ore genesis in these deposits is still unclear. The present study of the geochemistry of the REEs of these deposits is intended to improve genetic models. Materials and methods Three hundred samples were taken from above mentioned deposits. Samples were categorized into 5 groups: (1) fluorite ore types, (2) ore-stage calcite, (3) carbonate host rocks, (4) basaltic rock around the deposits, and (5) shale of the Shemshak formation. Fourteen pure fluorite samples, 4 samples of pure calcite, 4 samples of carbonate host rock, 1 sample of basalt and 1 sample of shale were analyzed for REEs by ICP-MS at West Lab in Australia. Results Analytical data on fluorite from the Elika deposits show very low REE concentrations (0.5-18ppm), in calcite(0.5-3ppm) in carbonate host rocks – limestone (1.8-7ppm), and in dolomitic limestone 6.5ppm, compared with upper Triassic basalt (43ppm) and shale (261ppm). REE in fluorite of these deposits are strongly enriched (10 3 to 10 6 times) relative to normal sea water, ore stage calcite and carbonate host rocks, especially for mid-REEs (Eu, Gd) and heavy REEs (Lu, Yb, La/Yb=~0.05). Also, LREEs depletion (La/Sm= 2-10) and HREEs (La/Yb=0.01-0.08) relatively enrichment of fluorites compared with limestone (La/Sm=2.5-4, La/Yb=0.1-1.5) and dolomitic limestone (La/Sm=4.28, La/Yb=0.07-0.4) host rocks as well as positive Eu anomaly are the most important REEs signatures in fluorites. Fluorite elsewhere in the world with low total REE conten thas been interpreted to have a sedimentary origin (Ronchi et al., 1993; Hill et al., 2000; Sasmaz et al., 2005). Strong enrichment of REEs in fluorite and carbonate host rocks worldwide, relative to normal sea water indicates that diagenetic and/or hydrothermal processes have contributed to the process. Depletion of LREEs and moderately strong HREE enrichment in fluorite relative to carbonate host rocks is interpreted to be post-sedimentation (Ronchi et al., 1993;Hill et al., 2000). Thisis supported by the hydrothermal character of the fluorite in the Elika deposits and similarity between REE profiles and those of fluorine-rich MVT deposits with hydrothermal origin (Chesley et al.,1994; Bau et al., 2003). Positive Eu anomalies in fluorite elsewhere suggest deposition reduced conditions and temperatures~250°C (Bau et al., 2003; Sverjensky, 1989). The present study indicates that low total REEcontents in fluorite precipitated from reduced hydrothermal solutions could be caused by (1) increasing pH of the ore-forming solution during interaction with carbonate host-rock, (2) gradually decreasing F concentration in hydrothermal solutions due to different generations of fluorite mineralization, and (3) low REE contents of carbonate hostrocks. References Bau, M., Romer, R.L., Luders, V. and Dulski, P., 2003. Tracing element sources of hydrothermal mineral deposits: REE and Y distribution and Sr-Nd-Pb isotopes in fluorite from MVT deposits in the Pennine Orefield, England. Mineralium Deposita, 38(8): 992–1008. Chesley, J.T., Halliday, A.N., Kyser, T.K. and Spry, P.G., 1994. Direct Dating of MississipValley-type mineralization: Use of Sm-Nd in fluorite. Economic Geology, 89(9):1192-1199. Hill, G.T., Campbell, A.R., and Kyle, P.R., 2000. Geochemistry of southwestern New Mexico fluorite occurrences: implications for precious metals exploration in fluorite-bearing systems. Journal of Geochemical Exploration, 68(1): 1–20. Ronchi, L.H., Touray, J.C., Michard, A. and Dardenne, M.A., 1993. The Riberia fluorite district, Southern Brazil. Geological and geochemical (REE, Sm–Nd isotopes) characteristics. Mineralium Deposita, 28(1): 40–52. Sasmaz, A., Yavuz, F., Sagiroglu, A. and Akgul, B., 2005. Geochemical patterns of the Akdagmadeni (Yozgat, Central Turkey) fluorite deposits and implications. Journal of Asian Earth Sciences, 24 (3): 469–479. Sverjensky, D.A., 1989. The diverse origins of Mississippi Valley-type Zn–Pb–Ba–F deposits. Chronicle of mineral research and exploration, 495(1): 5 – 13. Vahabzadeh, G., Khakzad, A., Rasa, I. and Mosavi, M.R., 2009. Study on S isotopes in galena and barite of Savad Kuh fluorite deposits. Journal of Basic Science, Islamic Azad University, 69(18): 99-108 (in Persian).

Mineralogical signature of nonsulfide zinc ores at Accha (Peru): A key for recovery

The general lack of a correlation between earthquakes and surface faulting in the interior of the western U.S. cordillera has motivated our efforts to evaluate the geometry, structural style, and mechanism of normal faulting characteristic of this region of intraplate extension. To address the problem, we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust. Rheological models of the continental crust were calculated to examine the possibility of shallow, quasi‐plastic flow and its influence on faulting in the eastern Basin‐Range, the western Colorado Plateau, and the Middle Rocky Mountains. Our data and interpretations have revealed the following styles of Cenozoic deformation: (1) steep‐ to low‐angle dip, normal faulting along the Wasatch fault, (2) low‐angle dip and listric normal faulting possibly associated with movement on preexisting thrusts, (3) the occurrence of asymmetric, mostly eastward tilted Tertiary basins that are bounded by low‐ to moderate‐dipping planar and listric faults, and (4) at least three vertically stacked, en echelon low‐angle reflections in the mid to upper crust that dip gently westward from ∼3 km beneath the Wasatch Plateau to over ∼15 km at the Utah‐Nevada border; these reflections are interpreted as normal detachment faults. The structural style of the pervasive low‐ to moderate‐angle dipping faults cannot be easily reconciled with classic brittle failure theory, but the interpreted termination of normal faults at or above the deeper low‐angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip. An important observation, based on interpretations of seismic reflection profiles, is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits. Segment boundaries of the Wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the Precambrian Uinta aulacogen, suggesting that preexisting crustal structure partly controls the geometry of extension. To examine the influence of ductile deformation, quasi‐plastic flow was modeled for appropriate geotherms of the Basin‐Range and Colorado Plateau crusts. These models provide constraints on the depth to the frictional/quasi‐plastic transition that occurs as shallow as ∼8 km in the eastern Basin‐Range. This depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes (M<5.5) occur and suggests the presence of a low shearing strength layer in which low‐angle faulting may be accommodated. Larger magnitude earthquakes (M>5.5) appear to nucleate at 10–15 km in or near the brittle/ductile transition. The rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region. Large‐scale low‐angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility.

Style and sequence of deformation during extensional fault-propagation folding: examples from the Hammam Faraun and El-Qaa fault blocks, Suez Rift, Egypt

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Landsat-8 data were integrated with geological data to map lithologic units, lineament features, hydrothermal alteration zones, and distribution of Fe3+-bearing minerals in the Zarshuran Carlin-type gold deposit. The dominant hydrothermal alterations related to the gold mineralization in the study area, consist of argillic, alunite, silicified, and decalcified alterations of carbonate host rocks. The alteration assemblages are accompanied by ferric iron minerals such as jarosite and hematite. The red-green-blue (RGB) combination of bands 5, 2, and 1 of the ASTER sensor provides excellent criteria for the separation of the host rock lithologic boundaries, particularly for the Oligo-Miocene andesitic volcanic rocks covering the vast parts of the study area. The ASTER lithologic map derived from RGB combination of bands 5, 2, and 1 is represented by a set of lineaments in which both the thrust and normal faults were enhanced. The band ratios obtained by the Landsat-8 and the ASTER datasets have been effectively used to delineate the alteration halos characterized by kaolinite, alunite, quartz, and ferric iron minerals both in regional and local (the Zarshuran gold mine) scales. In addition, methods such as the principal component analysis (PCA) and the selective principal component analysis (Crosta) were exerted on the ASTER data to identify the hydrothermal alteration zones. The spectral angle mapper (SAM) algorithm using the ASTER data could better differentiate the various alteration (e.g., argillic, alunite, and silicified) zones existing in the study area. The matched filtering (MF) technique processed on the Landsat-8 data was applied to characterize the ferric iron minerals (jarosite and hematite) and separate the hydrothermal alteration zones as well. The integration and combination of various image processing techniques indicated that the alteration zones at Zarshuran are affiliated with normal faults within the carbonate host rocks and can be used for prospection mapping purposes in regional scale.

We combined field mapping, structural and microstructural analyses, stable‐clumped isotope geochemistry, and U‐Pb dating of calcite veins and syn‐tectonic slickenfibres, to assess the regional scale fault‐related fluid flow during the evolution of the External Hellenides fold‐and‐thrust belt. We show that fluid circulation during forebulge uplift was characterized by cold meteoric water‐derived fluids, from which calcite precipitated and sealed bed‐perpendicular joints. Fluid circulation during foreland flexuring and early layer‐parallel shortening was characterized by warm fluids buffered by the carbonate host rock, which circulated through normal faults and bed‐parallel veins. Mixing with meteoric‐derived fluids also occurred at this stage of tectonic evolution. Fluid circulation during the late stage of thrust wedge accretion and post‐orogenic extension at 1.6 ± 1 Ma was characterized by increasing dominance of cold meteoric water circulating in strike‐slip and normal faults. The ingress of meteoric‐derived fluids was controlled by throughgoing fault conduits, while host rock‐buffered fluids were confined in isolated structures such as minor faults and veins. We developed a conceptual model of fault‐related fluid circulation, which invokes a transition from an open fluid system during forebulge uplift, to a semi‐closed fluid system during foreland flexuring and early layer‐parallel shortening, and to an open system during late thrust wedge accretion and post‐orogenic extension. This type of fluid circulation may have impacted fluid migration/leakage, including hydrocarbons, into or outside potential reservoirs in the highly prospective Hellenides‐Albanides fold‐and‐thrust belt, a renovated frontier for hydrocarbon exploration in the Mediterranean area.

Thirteen seismic reflection lines were processed and interpreted to determine the southern terminations of the Lost River and Lemhi faults along the northwest boundary of the eastern Snake River Plain (ESRP). The southernmost terminations of the Arco and Howe segments were determined to support characterization of the Lost River and Lemhi fault sources, respectively, for the INL probabilistic seismic hazard analysis. Keywords:Keywords are required forExternal Release Review*Keywords  Keywords *Contacts (Type and Name are required for each row) Type ofContactContact Name POC Editor RecordFour commercial seismic reflection lines (Arco lines 81-1 and 81-2; Howe lines 81-3 and 82-2) were obtained from the Montana Power Company. The seismic data were collected in the early 1980’s using a Vibroseis source with station and shot point locations that resulted in 12-fold data. Arco lines 81?1 and 81?2 and Howe lines 81?3 and 82?2 are located within the basins adjacent to the Arco and Howe segments, respectively. Seven seismic lines (Arco lines A1, A2, A3, and A4 and Howe lines H1, H2, and H3) were acquired by EG&G Idaho, Inc. Geosciences for this study using multiple impacts with an accelerated weight drop source. Station and shot point locations yielded 12-fold data. The seismic reflection lines are oriented perpendicular to and at locations along the projected extensions of the Arco and Howe fault segments within the ESRP. Two seismic lines (Arco line S2 and Howe line S4) were obtained from Sierra Geophysics. In 1984, they acquired seismic reflection data using an accelerated weight drop source with station and shot point locations that yielded 6-fold data. The two seismic reflection lines are oriented perpendicular to and at locations along the projected extensions of the Arco and Howe fault segments within the ESRP. In 1992 for this study, Geotrace Technologies Inc. processed all of the seismic reflection data using industry standard processing techniques. The southern termination of the Howe segment of the Lemhi fault was placed between Howe lines H1 and H2, 2.2 km south of the fault’s southernmost surface expression. In the adjacent basin, south-dipping normal faults at the northern end of Howe line 81-3 and two southwest-dipping normal faults at the northeastern end of Howe line 82-2 that can be correlated with Howe segment. South of the surface expression, two southwest-dipping normal faults on Howe line H1 can be correlated with the Howe segment. Further into the ESRP, Howe lines H2, H3, and S4 show continuous flat lying reflectors and indicate no fault offset. The southern termination of the Arco segment of the Lost River fault was placed between Arco lines S2 and A3, a distance of 4.6 km south of the fault’s southernmost surface expression. Within the basin, west-dipping normal faults interpreted on Arco lines 81-1 and 81-2 can be correlated with the Arco segment. Further south within the Arco volcanic rift zone (VRZ), three seismic lines (Arco lines A2, S2, and A3) permit two interpretations. The west- and south-dipping normal faults on Arco lines A2 and S2 could be associated with slip along the Arco segment. These normal faults have an opposite dip to an east-dipping fault on Arco line A3. The observed small-offsets (< 85 m) along the oppositely dipping normal faults can be interpreted as a graben structure that resulted from dike intrusion within the Arco VRZ. Arco line A4 further south within the Arco VRZ shows flat lyin

We developed velocity models to prestack depth migrate two seismic lines acquired in an area of complex mountainous geology in southern Alberta, Canada. Initial processing in the time domain was designed to attenuate noise and enhance the signal in the data. The prestack and poststack time-migrated sections were poorly focused, implying the velocity models would be inadequate for prestack depth migration. The velocity models for prestack depth migration, developed by flattening reflections on common image gathers, ineffectively imaged the complex geology. We developed our most effective velocity models by integrating the mapped surface geology and dips, well formation tops, geological cross sections, and seismic-velocity information into the interpretation of polygonal areas of constant velocity on several iterations of prestack depth-migrated seismic sections. The resulting depth-processed sections show a more geologically realistic geometry for the reflectors at depth and achieve better focusing than either the time-migrated sections or the depth sections migrated with velocity models derived by flattening reflections on offset gathers.

In many basins and especially those in NW Europe, 3D seismic data have become a necessary prerequisite to development, appraisal and, almost routinely, exploration drilling, but equally they are rarely seen as being sufficient. Why is this, when the majority of industry analysts recognize the value of 3D seismic data to an oil company’s exploration portfolio: are geophysicists too successful at marketing? Are we victims of promising too much, or should we see this hunger for ever more subsurface information as encouragement to refine existing technologies further and to develop new ones? In September 2002, the Geological Society meeting on exploration in volcanic margins heard about a successful strategy of ‘drilling the bumps’, which led to the discovery of the Marjun hydrocarbon accumulation, the first in Faroese waters. Petex 2002 was told that the biggest UK North Sea discovery for a decade had not used ‘geophysical malarkey’. Is seismic technology inadequate, or has it reached its limits as the targets get ever tougher? Evidently, as the remaining basins become covered by seismic surveys, the easy finds are becoming fewer. Having consumed roughly half the world’s proven reserves, new reserves must be found using ever more imaginative geological hypotheses, and remote sensing technologies will need to give access to ever more information and provide discrimination to test the hypotheses and reduce the risk. The quest for resolution is unrelenting and finer spatial sampling is providing significant improvements in imaging. Honouring well information requires more realistic, anisotropic velocity models for pre-stack depth migration which furnish images that are better representations of the drillable geology. The need to qualify the data in a seismic survey has resulted in so many auxiliary measurements of the acquisition system itself that the subsurface data are almost in a minority, but this brings improved, quantified repeatability, with the potential to drive down time-lapse seismic noise and reveal subtle, production-related reservoir changes. Qualified amplitudes and careful control during processing allow inversion for elastic parameters of the subsurface. With good petrophysical and geomechanical models, elastic inversions can benefit both the reservoir engineer and the driller and offer further potential for multi-component acquisition in reservoir characterization. Salt, basalt or complex tectonic overburdens pose their own challenges to imaging and encourage potential field measurements to complement seismic data in velocity model building and the prediction of reservoir rocks or fluids. Very long offsets and very low seismic frequencies may also have a rô le to play in these environments. Breakthroughs in data handling and visualization technology allow us to take full benefit of these improvements. The stimulus for innovation is as strong as ever and, even if the immediate economic context is uncertain, the industry is responding. This paper will review several of the current technology trends and offer some speculation on the road ahead.

Propagation, interaction and linkage in normal fault systems

Gangue minerals from hydrothermal deposits (apatite and carbonates) and their host rocks from three different volcanic areas (SE Spain, La Serena and Melipilla in Coastal Range of Chile) have been studied for broad elemental compositions. Carbonate units at the Au-Cu Palai-Islica epithermal deposit are Fe-Mn-bearing, with a slightly higher concentration of these elements in the orebody than in adjoining hydrothermal alteration zones. Apatite has a composition that correlates with its origin and with hydrothermal processes. Thus, volcanic apatite is Cl-rich, whereas apatite from the associated orebody is almost pure fluorapatite. Furthermore, apatite from hydrothermally altered volcanic rocks has a transitional composition between volcanic and ore-related apatite. Samples of carbonate from Mn, Cu(-Ag) and Ba-Ag deposits in the La Serena area are all Mn-bearing calcite. In addition, Mn(Fe)-poor and Mg-rich calcite is common in low-grade Mn areas. Similar features have been found at the Melipilla Cu (Cu-Ag) deposit where epithermal calcite is also enriched in Mn(+Fe) with respect to non-mineralized veins, carbonate host rock, and metamorphic mineralization. In summary, F in apatite and Mn have been introduced in to carbonate from the La Serena area by hydrothermal fluids and could provide an index of hydrothermal ore-forming activity.KeywordsHydrothermalganguecarbonateapatiteSpainChile

Alteration, mineralization, and genesis of the Lietinggang–Leqingla Pb–Zn–Fe–Cu–Mo skarn deposit, Tibet, China

One of the aims of the ICDP Drilling the Ivrea-Verbano zonE project (DIVE) is to unravel lithological drivers of geophysical observations in the lower continental crust. During Phase I of the project, two boreholes, 5071_1_B and 5071_1_A, have been completed at depths of 578.5 and 909.5 m in December 2022 and March 2024, respectively. Borehole 5071_1_B is drilled into the upper part of the lower continental crust, while borehole 5071_1_A extends deeper into the lower crust. Core descriptions identified the lithologies in borehole 5071_1_B as kinzigite, amphibolite, calcsilicate and leucosome. In contrast, borehole 5071_1_A encountered a variety of lithologies including stronalite, anorthosite, gabbro, garnetite, gabbronorite, garnet granulite and pyroxenite. Together, these two boreholes represent a comprehensive cross-section of the lower continental crust in the Ivrea-Verbano zone. To understand the geophysical characteristics and their correlation to lithologies, a comprehensive set of geophysical borehole logs was acquired, including among others spectral gamma ray, magnetic susceptibility, sonic, acoustic and optical televiewer data. To complement the downhole data set, core density and magnetic susceptibility measurements were conducted using a multi-sensor core logger. In our previous study, fuzzy c-means clustering of magnetic susceptibility and natural gamma logs from borehole 5071_1_B demonstrated an excellent agreement with the lithological core description, despite notable spatial variability. In this study, we integrate the petrophysical data from both boreholes revealing significant contrasts in petrophysical properties between them. Preliminary results indicate that the rocks in 5071_1_A generally exhibit lower gamma radiation, higher densities and higher velocities compared to those in 5071_1_B, with the exception of some amphibolite intervals in 5071_1_B. With respect to their magnetic susceptibilities the lithologies of both boreholes partially overlap; however, gabbros, gabbronorites and garnet granulites exhibit significantly higher average susceptibilities with values up to 10-1 SI. Most of the stronalites in borehole 5071_1_A exhibit gamma ray values comparable to the lower range observed in 5071_1_B, whereas gamma ray values for all other lithologies in 5071_1_A are generally lower than those in 5071_1_B. These findings suggest that gamma ray and magnetic susceptibility data may also act as good lithological indicators when analysing the combined data set. Core density measurements further complement this analysis, with values ranging between 2.8 and 3.4 g/cm3 in 5071_1_A, compared to 2.5 to 2.8 g/cm3 in 5071_1_B. The P-wave velocity of 5071_1_A predominantly ranges from 6000 to 7000 m/s, exceeding those observed in borehole 5071_1_B where velocities are strongly influenced by brittle deformation rather than lithological factors. Although numerous fractures are encountered in 5071_1_A, an initial analysis suggests correlations with lithological variations, as evidenced by high P-wave velocities exceeding 7000 m/s in a pyroxenite section. This implies that seismic reflections in 5071_1_A may be attributable to lithological velocity contrasts. To further investigate the origins of seismic reflectivity in these rocks, an acoustic impedance profile for both boreholes is required. This will help evaluate the influence of brittle deformation and lithological variations on seismic reflectivity.   

Seismic acquisition and processing for imaging the subsurface is an important workflow in the petroleum industry. Complex geological settings such as tectonic thrust belts are a major challenge. The Sierra de Reyes 3D (SR3D) seismic survey in western Argentina is an example of where rough terrain land acquisition is combined with complex structural geology. These two problems have to be solved concurrently during the depth imaging steps. The SR3D land seismic project (270 km2) is located in the SE part of the Ranquil Norte concession (Neuquen Basin, Figure 1). The area lies in the Southern Central Andes, in the external Malargue fold and thrust belt (FTB). The FTB is characterized by the coexistence of thick and thin skin thrusting. This compressive regime has produced the structural traps of several main oil and gas fields of the northern Neuquen Basin. The further exploration of this hydrocarbon play has driven the development of the SR3D project (Figure 2).

Normal faults are not simple planar fractures, but consist of complex zones of overstepping and linked segments. This paper emphasizes the ubiquity of fault segmentation and its importance in the geometry and development of normal faults. Normal fault segments usually initiate as extension fractures in more brittle layers, with faulting occurring as the fractures propagate into the adjacent less brittle layers. Relay ramps are areas of reorientated bedding between two normal fault segments which overstep in map view and which dip in the same direction. Relay ramps can be important sites for hydrocarbon migration and entrapment. Oversteps and bends also occur along normal faults in cross-section, these often being controlled by lithological variations. Normal faults therefore have complex three-dimensional geometries of interacting and linked segments.