Preliminary Geological Model Research Articles

Geological-technical study for the design of an underground variant of S.S. 52 “Carnica” in the Passo Mauria area (Carnic Alps)

This study aims to define a preliminary geological model of the Passo Mauria tunnel, designed as an alternative underground route to the current S.S.52 to ensure a safer connection over the top way Belluno (A27 Highway) Tolmezzo (A23 Highway), on which various tourist and economic activities revolve. The survey stage has allowed us to describe and represent the cartographic elements that describe the geology of the study area. The study has mainly focused on the investigation of the presumed entrances of the tunnel, characterized by specific geological and geomorphological conditions. The aerial photogrammetric survey supported the reconstruction of the geometry of discontinuities in the non- accessible areas. Besides, this study has allowed the definition of the possible behaviour of the rock mass subjected to the tunnel excavation and of sections with homogeneous mechanical properties. The drafting of a survey plan supplements the study to determine a geological and geotechnical model, for the subsequent investigation and design phases.

Surface and borehole geophysics for the rehabilitation of a concrete dam (Penne, Central Italy)

In this paper, surface and borehole geophysical surveys are employed to improve the effectiveness of a rehabilitation intervention (cut-off wall) to be executed on the right abutment of a leaking concrete dam (Penne, Central Italy). In a first step, surface geophysical measurements (electrical resistivity and P-wave velocity data), were collected to provide a geophysical model to be compared to the preliminary geological model available before the geophysical survey. Because significant differences emerged between the geophysical and the preliminary geological models, a second phase of borehole investigations was planned to validate the geophysical reconstruction obtained from surface data. The final geological model resulting from the geophysical results differs significantly from the preliminary model available at the time of the geophysical survey. Therefore, the planned cut-off wall needs to be extended both laterally and in depth beyond the position estimated before the geophysical campaign, so that the low-permeability bedrock is intercepted at a depth equal or lower than the critical one. At the end, the low-cost geophysical campaign (1.5% of the entire costs of the intervention) was highly beneficial to this project, minimizing subsurface geological uncertainty to design an effective anti-seepage intervention and stressing the importance of a representative geological model for engineering design.

The distribution of deep source rocks in the GS Sag: joint MT–gravity modeling and constrained inversion

The coal-bearing strata of the deep Upper Paleozoic in the GS Sag have high hydrocarbon potential. Because of the absence of seismic data, we use electromagnetic (MT) and gravity data jointly to delineate the distribution of deep targets based on well logging and geological data. First, a preliminary geological model is established by using three-dimensional (3D) MT inversion results. Second, using the formation density and gravity anomalies, the preliminary geological model is modified by interactive inversion of the gravity data. Then, we conduct MT-constrained inversion based on the modified model to obtain an optimal geological model until the deviations at all stations are minimized. Finally, the geological model and a seismic profile in the middle of the sag is analysed. We determine that the deep reflections of the seismic profile correspond to the Upper Paleozoic that reaches thickness up to 800 m. The processing of field data suggests that the joint MT–gravity modeling and constrained inversion can reduce the multiple solutions for single geophysical data and thus improve the recognition of deep formations. The MT-constrained inversion is consistent with the geological features in the seismic section. This suggests that the joint MT and gravity modeling and constrained inversion can be used to delineate deep targets in similar basins.

Impact of Geophysics in Small-Scale Mining

Geological exploration for new mining ventures involves drilling campaigns, an expensive activity that may take significant time, with no guarantee of financial success. The literature review indicated that the average cost of drilling may reach over US $100 per meter drilled, and that the use of Geophysics can reduce by 30% to 50% the number of negative drill holes (holes that does not intercept the mineral orebody), thus reducing time and cost of mineral exploration. This paper shows how the application of Geophysics in two small-scale mining operations, a limestone and manganese mine, resulted in reduced exploration time with satisfactory results for the companies. In the limestone mine, Geophysics allowed the updating of the geological model. In the manganese mine, it contributed to the generation of a preliminary geological model for the deposit. In both cases, there was a significant reduction of the time spent on exploration.

TWO EXAMPLES FOR IMAGING BURIED GEOLOGICAL BOUNDARIES: SINKHOLE STRUCTURE AND SEYİT HACI FAULT, KARAPINAR, KONYA

Once anomalies with positive and negative circular closures are assessed together in potential field maps, the ones which have meaningful geometric structure appear as more distinguishable. When the edge detection is applied, the preliminary geological model about the geological structure may or may not be verified. When it is not verified then it is understood that the predicted geological model should be reconsidered and discussed again. In this study, the edge detection was introduced and the success of the method was tested in an artificial data. Following that, its effect on sinkholes was studied applying the method on detailed gravity data collected in Karap›nar (Konya) region. At the same time, this method was applied on data related to active Seyit Hac› Fault zone. It was detected that the fault had shown continuity towards SW and these evidences were discussed.

Influence of the antiformal setting on the kinematics of a large mass movement: the Passo Vallaccia, eastern Italian Alps

The article examines the influence of antiformal settings on the evolution of alpine slopes using 2D numerical modelling. The northern slope of the Upper Vizze Valley, which follows a huge antiform involving meta-granitic and meta-sedimentary rocks, is affected by a complex gravitational phenomenon mainly controlled by the attitude of the foliation. A preliminary geological model based on field surveys was refined using the results of 2D distinct element numerical modelling. In the crown area, the sub-horizontal meta-sedimentary sequence at the fold hinge is cut by sharp planes, whilst in the middle zone the sequence was passively dragged downwards and finally, in the lowest part of the slope, corresponding to the steeply dipping antiformal flank, the deformation propagated across the entire meta-sedimentary succession through strain partitioning along multiple shear surfaces.

Deriving geological contact geometry from potential field data

The building process of any geological map involves linking sparse lithological outcrop information with equally sparse geometrical measurements, all in a single entity which is the preferred interpretation of the field geologist. The actual veracity of this interpretative map is partially dependent upon the frequency and distribution of geological outcrops compounded by the complexity of the local geology. Geophysics is commonly used as a tool to augment the distribution of data points, however it normally does not have sufficient geometrical constraints due to: a) all geophysical inversion models being inherently non-unique; and b) the lack of knowledge of the physical property contrasts associated with specific lithologies. This contribution proposes the combined use of geophysical edge detection routines and ‘three point’ solutions from topographic data as a possible approach to obtaining geological contact geometry information (strike and dip), which can be used in the construction of a preliminary geological model. This derived geological information should first be assessed for its compatibility with the scale of the problem, and any directly observed geological data. Once verified it can be used to help constrain the preferred geological map interpretation being developed by the field geologist. The method models the contacts as planar surfaces. Therefore, it must be ensured that this assumption fits the scale and geometry of the problem. Two examples are shown from folded sequences at the Bathurst Mining Camp, New Brunswick, Canada.

Preliminary geology, mineral chemistry and diamond results from the C29/30 Candle Lake volcanic complex, Saskatchewan, Canada

The C29/30 kimberlite is one of two diamondiferous kimberlites in the Candle Lake cluster located in east-central Saskatchewan, Canada, approximately 70 km from the Fort á la Corne kimberlite field. The kimberlites are hosted by a Cretaceous sequence of marine mudstone and shale of the Lower Colorado Group, and underlying siltstone and sandstone of the Mannville Group. This sequence overlies Paleozoic carbonates that were deposited over the Proterozoic crystalline basement. Based on the country rock stratigraphy and morphology of the body, C29/30 is inferred to be Cretaceous in age. The elongated kimberlite body has a lateral extent of approximately 2 km with the long axis oriented in a south-east to north-west direction and an estimated surface expression of 75.3 ha. The investigation of 47 drill cores suggests that this body is a single volcanic complex dominated by a single phase of volcaniclastic kimberlite that is characterised by absent to rare phlogopite within the groundmass of preserved juvenile clasts. Minor amounts of at least one other phase of kimberlite containing conspicuous groundmass phlogopite have also been documented. The subsurface shape of C29/30 is complex and is interpreted to result from a combination of explosive volcanic activity that formed two craters from separate feeder vents. The formation of the elongated trough is poorly understood. It may have formed by a fissure style eruption, or erosive processes related to the mass flow of material away from one of the craters or possible the collapse of an eruption column. The C29/30 kimberlite is similar to bodies of the Fort á la Corne kimberlite field with respect to country rock setting, pipe morphology and the dominant textural varieties present. This contribution presents a preliminary geological model of C29/30 based on data obtained from the drilling programmes completed in 2006, 2007 and 2008.

Geologic Setting and Gas Reserves of the Venezuelan LNG Project

Four gas fields, Mejillones, Patao, Dragon, and Rio Caribe, were discovered by Lagoven, a subsidiary of Petroleos de Venezuela S.A., during an exploratory campaign during 1978-1982, offshore northeastern Venezuela. Thirteen wells drilled in the four fields discovered 13.9 tcf of gas, including 1.2 tcf of gas and condensate in the Rio Caribe field. In February 1991, Lagoven entered into an agreement with Shell, Exxon, and Mitsubishi to assess the viability of producing and exporting gas from the four offshore gas fields in the form of liquified natural gas. This is the Venezuelan LNG Project, otherwise called the Cristobal Colon Project. As part of the agreement the participants established a Project Team in Caracas and undertook the acquisition of 1600 km[sup 2] of 3D seismic data over the four fields to evaluate the geological model of the area. In addition, interpretation of the 3D data has led to a preliminary geological model for the gas bearing sands which envisages deposition in a regional setting varying from bathyal turbidites in the Rio Caribe and Mejillones fields in the west to shelf deposits over the Patao and Dragon fields in the east. In addition to the geological setting this paper will discuss preliminarymore » results of the reserves evaluation for the Rio Caribe, Patao, and Dragon fields.« less

Geological model for Boulder 1 at Station 2, South Massif, Valley of Taurus-Littrow

It appears possible to establish a preliminary geological model for the origin and evolution of the breccias of Boulder 1 at Station 2 in the Valley of Taurus-Littrow based on firm and probable geological constraints. The crystallization of plagioclase and other ANT-suite phases now present as clasts appears to have occurred in the lunar crust about 4.5 b.y. ago during the ‘melted shell stage’ of lunar history as that history is presently modeled. The original rocks containing these phases, which now make up the gray competent breccias of Boulder 1, were greatly modified by impact processes during the ‘cratered highland stage’ and the early part of the ‘large basin stage’, up to about 4.0 b.y. ago. About 4.0 b.y. ago, pigeonite basalts with KREEP affinities appear to have been intruded into the pre-Serenitatis crust from which the light friable breccias of Boulder 1 were later derived.