The geothermal gradient map of Central Tunisia: Comparison with structural,gravimetric and petroleum data

Five hundred and fifty temperature values, initially measured as either bottom-hole temperatures (BHT) or drill-stem tests (DST), from 98 selected petroleum exploration wells form the basis of a geothermal gradient map of central Tunisia. A “global-statistical” method was employed to correct the BHT measurements, using the DST as references. The geothermal gradient ranges from 23° to 49°C/km. Comparison of the geothermal gradient with structural, gravimetric and petroleum data indicates that:

• 1.(1) the general trend of the geothermal gradient curves reflects the main structural directions of the region,
• 2.(2) zones of low and high geothermal gradient are correlated with zones of negative and positive Bouguer anomalies and
• 3.(3) the five most important oil fields of central Tunisia are located near the geothermal gradient curve of 40° C/km.

Such associations could have practical importance in petroleum exploration, but their significance must first be established through further investigation and additional data.     

Aridification — Climate change in South-Eastern Europe

Climatic change in SE Europe can be characterized by the term aridification, which means increasing semi-aridity, manifested in an increase of mean annual temperature and at the same time in a decrease in the yearly precipitation.The paper deals with research results obtained within the framework of the MEDALUS II project (funded by the Commission of the European Communities). The project had the following objectives:

• 1.(i) Assessment of the impact of global change on the climate of the investigated area, including possible future climates.
• 2.(ii) Physical processes of aridification, including studies of groundwater level change, soil moisture profile dynamics, soil development, vegetation change and soil erosion.
• 3.(iii) Land use change, involving research on present land use and suggestions for the future.

Various methods were applied with respect to the different research objectives.

• 1.(i) Statistical analysis of climatic oscillations and computer runs of climatic scenarios,
• 2.(ii) Analysis of ground water data, mapping and analysis of soils and vegetation, assessment of present and future soil, and
• 3.(iii) Land capability assessment through ranking environmental conditions according to the demands of the most widely grown arable crops in Hungary.

According to our results i) the average annual warming during the last 110 years was +0.0105 °C, and precipitation decreased by 0.917 mm/year; ii) a decline of −2 to −4 m in the annual mean groundwater level can be detected in the most sensitive areas, with gradual lowering of the water table in alkali ponds; complete desiccation of some of them severs the direct contact between groundwater and salt-affected soils, the solonchak soil dynamics cease, helophile and hygrophile plant associations disappear, and consequent changes in the soil erosion regime are likely to lead to disastrous erosion in the future; iii) the climatic changes induce a transformation in land use from arable crops to plantations, starting with orchards.     

Groundwater development,Kharga Oases,Western Desert of Egypt: A long-term environmental concern

The groundwater reserves in Kharga Oases have been studied for the long-term socioeconomic development in the area. The Nubian Sandstone, which consists of a thick sequence of coarse clastic sediments of sandstone, sandy clay interbedded with shale, and clay beds, forms a complex aquifer system. The Nubian Aquifer has been providing water to artesian wells and springs in the Kharga Oases for several thousand years. Groundwater in the Kharga Oases is withdrawn from springs and shallow and deep artesian wells Nearly all the wells originally flowed, but with the exploitation of ground-water from deep wells for irrigation beginning about 1959. the natural flows declined as more and more closely spaced deep wells were drilled By 1975 many deep wells had ceased to flow The water demand in the area has been met by pumping both shallow and deep wells The total annual extraction from deep wells has fluctuated over the year, however, the annual withdrawal from deep wells has exceeded extraction from shallow wells About 17 billion m³ of water was withdrawn from the combination of shallow and deep wells during the period 1960–1980 The Nubian complex aquifer in the Kharga Oases has a very large groundwater potential that could be exploited and beneficially used for a long-term agricultural development in the area, provided proper well spacing and management are implemented Other major environmental considerations for which precise hydrogeologic data are needed include

1. Determination of the long-term yield available from properly constructed and producing artesian wells that will support a planned migration of population from the overcrowded Nile delta and flood plain areas
2. Development of an effective management program and adequate staff to maintain groundwater production over an extended period of years
3. The impact on climate caused by extensive irrigation in the oases of the Western Desert of Egypt
4. Protection against water logging of soils from irrigation practices
5. Protection against salinization of soils from irrigation practices
6. Development of effective surface and subsurface drainage practices
7. The impact of farming and pest control practices on the shallow groundwater of the oases
8. Determination of the long-term development of the artesian water on the quality of the water from the aquiter systems in the Western Desert

This paper addresses items 1, 2 and 8.     

Seismic patterns in Northern China and the characteristics of the epicentral distribution of the medium strong earthquakes before the large events

In this paper, the seismic pattern in Northern China from 30 ° to 42 ° N latitude and 104 ° to 125 ° E longitude, and the characteristics of the epicentral distribution before large events are presented. The results suggest that:

• 1.(1) the earthquakes in the region are mainly located in the orthogonal curvilinear network formed by the seismic belts;
• 2.(2) the larger earthquakes (M ⩾6) occurred mainly in the nodal regions of this grid:
• 3.(3) the strike of the fracture planes of the earthquakes coincided with the directions of the seismic belts;
• 4.(4) the pattern of medium strong earthquakes (M ⩾ 4.7) prior to thirteen large earthquakes (M⩾ 7) are analysed to be of three types:
  • 4.1.(a) mainly arranged along the two intersecting belts,
  • 4.2.(b) randomly distributed,
  • 4.3.(3) forming seismic gaps.

A theoretical basis and rules for drawing the orthogonal grid is presented, and an idea for the prediction of the sites of future earthquakes in Northern China is suggested.     

A quantitative fluorescence technique for evaluating thermal maturity: Instrumentation and examples

Fluorescence microscopy is useful not only for identifying most of the oil-prone organic matter (macerals) in sedimentary rocks and coals but also for assessing their thermal maturities (ranks). This report introduces a violet-light excitation system which induces more than one order of magnitude stronger fluorescence intensity that the commonly used UV-light excitation system. The red/green quotient from violet-light excited fluorescence, Q_v, of sporinite can be easily measured using this system. Several examples using coal and cuttings samples are presented to demonstrate the use of this technique for evaluating the thermal maturities of coals and sedimentary rocks.From the results of our studies we conclude that:

• 1.(1) Violet-light excited fluorescence from sporinites can be routinely measured to assess thermal maturity.
• 2.(2) Spectral (Quantitative) fluorescence technique is useful for evaluating thermal maturity when samples are poorly polished or deficient in vitrinite.
• 3.(3) Visual (Strew-mounted) kerogen slides can not be used for fluorescence measurements unless a non-fluorescent mounting medium is used.

     

Mineralogy and petrology of alkaline granophyric xenoliths from the Thorsmörk ignimbrite,southern Iceland

The Thorsmörk ignimbrite, southern Iceland, contains a suite of granophyre xenoliths displaying magmatic or high-temperature sub-solidus mineral assemblages. These granophyres are consanguineous with the erupting comenditic magma. Four types of mineral assemblages are distinguished:

• 1.(A) oligoclase, edenitic hornblende, salitic pyroxene, magnesian biotite, magnetite and sphene;
• 2.(B) oligoclase, manganoan to sodic ferro-augite, fayalite, richterite, ilmenite and magnetite;
• 3.(C) anorthoclase, ferrohedenbergite to aegirine hedenbergite, ilmenite, magnetite and (riebeckite);
• 4.(D) cryptoperthite, aegirine hedenbergite to (aegirine), aenigmatite, arfvedsonite, ilmenite and magnetite.

Geothermometry shows that the xenoliths have crystallized between 900°C and 500°C at moderate oxygen fugacities, just above the FMQ buffer. It is further demonstrated that a hot vapour phase heavily charged with sodium and halogens, played a major role in the late sub-solidus crystallization of the different types.     

Great earthquakes,seismicity gaps and potential for earthquake disaster along the Himalaya plate boundary

Analysis of the space-time patterns of seismicity in the Himalaya plate boundary has established the existence of three seismic gaps:

• 1.(1) The “Kashmir gap” lying west of the 1905 Kangra earthquake;
• 2.(2) the “Central gap”, situated between the 1905 Kangra and the 1934 Bihar earthquakes;
• 3.(3) the “Assam gap” between the 1897 and 1950 Assam earthquakes.

This study has shown that the above great earthquakes were preceded as well as followed by long periods (⩾ 19 years) of decreased levels of seismic activity in the epicentral regions. Remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the Central gap as well as in the Assam gap. Local seismic investigation in the Assam gap confirms this feature and the seismicity suggests the existence there of an asperity.The local seismic investigations in Garhwal Himalaya have shown that the small earthquakes are confined to the upper 6–8 km of the crust and may have strike-slip motions. These earthquakes occur in a region where teleseismically recorded events were few.     

Development of engineering geology in western United States

Geologic concepts and scientific-technical guidance for the planning-design and construction of engineered works was recognized in Europe by the 1800s and by the early 1900s in North America. This early geologic knowledge and experience provided the rudimentary principles that guided practitioners of the 19th century in serving the emerging projects in western United States. Case studies review the scientific-technical lessons learned and the legacy of geologic principles established in the planning and construction of major civil, mining, and military engineered works in the western states. These contributions to GeoScience knowledge and engineering geology practice include:

• •Tunnels and aqueducts across active fault zones, beneath young volcanic features, groundwater-charged faults, and land subsidence mitigation.
• •Controversial foundation design, Folsom and Auburn dams, Golden Gate Bridge.
• •Protective underground construction chambers, safety dependent geologic setting.
• •Geologic mapping as database management leasing, maintenance railroad trackway.
• •Causeway Great Salt Lake, geo-risks calculated, mitigated ‘as-constructed’.
• •Nuclear powerplants seismic design.
• •Urban Land-Use, on-going processes, acceptable geo-risks.
• •Dwelling Insurance, insuree's responsibilities.
• •Selecting technique/method to mitigate risk, preferably based on extensive database, evaluation of characteristics and historical origin adverse features/conditions that constitute a geo-risk.

     

An alternative view of the Bayesian probabilistic prediction of strong shocks in the Hellenic Arc

A Bayesian discrete distribution, as developed by Ferraes (1985), is applied to predict the inter-arrival times for strong shocks in the Hellenic Arc on the basis of nine samples of shocks with seismotectonic locations very different from those used by Ferraes. The results suggest an alternative view of the Bayesian probabilistic prediction of strong earthquakes in the Hellenic Arc, and can be summed up as follows:

• 1.(a) Maximum final Bayesian probabilities of various inter-arrival times in a given seismotectonic segment are very dependent on the data set used and particularly on its time length.
• 2.(b) When using this method to determine the time intervals during which large shocks are to be expected in the Western and Eastern Hellenic arcs, it is very difficult to estimate intervals of less than a decade. The determination of the occurrence time, even in the long-term sense, remains the major problem in the prediction of these shocks.
• 3.(c) Bayesian probabilities in conjunction with seismicity observations indicate that large intermediate depth earthquakes in the Hellenic Arc are long overdue. Shocks of this sort can be expected to occur in the next few years.

It is also pointed out that although Bayesian-type predictions may be useful for engineering purposes, they are not a suitable basis for making specific predictions or taking special precautions.     

Multivariate mixing and mass balance (M3) calculations,a new tool for decoding hydrogeochemical information

To support and help hydrochemical evaluation a multivariate mathematical tool named M3 (Multivariate Mixing and Mass balance calculations) has been created within the Äspö Hard Rock Laboratory Research Programme. The computer code can be used to trace the origin of the groundwater and calculate the mixing portions and mass balances from ambiguous groundwater data. Groundwater composition data used traditionally to describe the reactions taking place in the bedrock can now be used to trace the effect from present and past groundwater flow with increased accuracy. The M3 model consists of the following 3 steps:

• •Multivariate analysis, called Principal Component Analysis (PCA) is used to summarise the information from the data set. The summarised information shown in the PCA plots is used for finding relationships, patterns, extreme waters and for further M3 modelling.
• •From the PCA plot mixing calculations are used to calculate the effect of the groundwater mixing on the obtained groundwater composition. This so-called ideal mixing model is used to calculate the mixing proportions given in %, for all the groundwater samples.
• •The final step in M3 calculations is the mass balance calculations. Deviations from the ideal mixing model are used to trace the sources and sinks of elements, given in mg/l, which can be due to mass balance reactions.

The tested margin of error of the model is ±10% for the Äspö site data, but depends on the data to be modelled. A mixing portion of less than 10% is regarded as under the detection limit of the model and such calculations are therefore uncertain. This method can be used to trace the origin and calculate the mixing portions and effects from the reactions on the observed groundwater composition with a higher resolution and convenience compared to many standard methods.     

The crustal structure of the axis of the Great Valley,California, from seismic refraction measurements

In 1982 the U.S. Geological Survey collected six seismic refraction profiles in the Great Valley of California: three axial profiles with a maximum shot-to-receiver offset of 160 km, and three shorter profiles perpendicular to the valley axis. This paper presents the results of two-dimensional raytracing and synthetic seismogram modeling of the central axial profile. The crust of the central Great Valley is laterally heterogeneous along its axis, but generally consists of a sedimentary section overlying distinct upper, middle, and lower crustal units. The sedimentary rocks are 3–5 km thick along the profile, with velocities increasing with depth from 1.6 to 4.0 km/s. The basement (upper crust) consists of four units:

• 1.(1) a 1.0–1.5 km thick layer of velocity 5.4–5.8 km/s,
• 2.(2) a 3–4 km thick layer of velocity 6.0–6.3 km/s,
• 3.(3) a 1.5–3.0 km thick layer of velocity 6.5–6.6 km/s, and
• 4.(4) a laterally discontinuous, 1.5 km thick layer of velocity 6.8–7.0 km/s. The mid-crust lies at 11–14 km depth, is 5–8 km thick, and has a velocity of 6.6–6.7 km/s. On the northwest side of our profile the mid-crust is a low-velocity zone beneath the 6.8–7.0 km/s lid. The lower crust lies at 16–19 km depth, is 7–13 km thick, and has a velocity of 6.9–7.2 km/s. Crustal thickness increases from 26 to 29 km from NW to SE in the model.

Although an unequivocal determination of crustal composition is not possible from P-wave velocities alone, our model has several geological and tectonic implications. We interpret the upper 7 km of basement on the northwest side of the profile as an ophiolitic fragment, since its thickness and velocity structure are consistent with that of oceanic crust. This fragment, which is not present 10–15 km to the west of the refraction profile, is probably at least partially responsible for the Great Valley gravity and magnetic anomalies, whose peaks lie about 10 km east of our profile. The middle and lower crust are probably gabbroic and the product of magmatic or tectonic underplating, or both. The crustal structure of the Great Valley is dissimilar to that of the adjacent Diablo Range, suggesting the existence of a fault or suture zone throughout the crust between these provinces.     

Location of the source and shallow velocity model deduced from the explosion quakes recorded by two seismic antennas at Stromboli volcano

The seismic wavefield associated to the ongoing eruptive activity at Stromboli volcano (Italy) is investigated using data from two small-aperture, short-period seismic arrays deployed on the northern and western flanks, located at about 1.7 km from the active craters. Two distinct approaches are used to analyze the recorded signals:

• 1.1) the zero-lag cross-correlation method is used to analyze the explosion quakes data, to estimate slowness and backazimuth as a function of lapse time;
• 2.2) multiple filter technique and phase matched filtering are used to estimate Rayleigh wave dispersion, to obtain a shallow velocity model of the two sites.

Estimates of slowness vectors at the two different array sites show a primary (volcanic) source located at shallow depth beneath the crater region. Secondary sources associated with path effects are located in close proximity of the sector graben of Sciara del Fuoco and of the old parasitic cone of Timpone del Fuoco. The shallow velocity structure derived for the western flank depicts striking resemblance with that previously inferred for the northern flank of the volcano.     

Measurements and interpretations of36Cl in groundwater,Milk River aquifer,Alberta, Canada

The³⁶Cl/Cl ratios of 12 groundwater samples from the Milk River aquifer were determined by accelerator mass spectrometry. Using known Cl concentrations,³⁶Cl concentrations were deduced. Approximately linear relations were observed between the logarithm of the³⁶Cl concentration, the Cl concentration, and the distance from the recharge area along two flow paths. The results are discussed in two approaches:

• (1)in an interpretation of the linear relation between logarithm of the³⁶Cl concentration and Cl concentration excluding and includingin situ production of³⁶Cl;
• (2)in a diffusion model. The increase of the Cl concentration with the distance from the recharge area is considered to be due to diffusion of Cl from the underlying confining Colorado shale to the aquifer.

Flow velocities ranging between 0.04 and 0.14 m/a, and ages of the groundwater between 0.6 and 2 Ma are obtained at a distance of 80 km from the recharge area.     

Ore mineralization related to geological evolution of the Karkonosze–Izera Massif (the Sudetes,Poland) — Towards a model

The Karkonosze–Izera Massif is a large tectonic unit located in the northern periphery of the Bohemian Massif. It includes the Variscan Karkonosze Granite (about 328–304 Ma) surrounded by the following four older units:

• -Izera–Kowary (the Early Paleozoic continental crust of the Saxothuringian Basin),
• -Ještĕd (the Middle Devonian to Lower Viséan sedimentary succession deposited on the NE passive margin of the Saxothuringian Terrane), out of the present study area,
• -Southern Karkonosze (metamorphosed sediments and volcanics filling the Saxothuringian Basin), out of the present study area,
• -Leszczyniec (Early Ordovician, obducted fragment of Saxothuringian Basin sea floor).

The authors present a genetic model of ore mineralization in the Karkonosze–Izera Massif, in which ore deposits and ore minerals occurrences are related to the successive episodes of the geological history of the Karkonosze–Izera Massif:

• -formation of the Saxothuringian Basin and its passive continental margin (about 500–490 Ma)
• -Variscan thermal events:
  • -regional metamorphism (360–340 Ma)
  • -Karkonosze Granite intrusion (328–304 Ma)
• -Late Cretaceous and Neogene-to-Recent hypergenic processes.

The oldest ore deposits and ore minerals occurrences of the Karkonosze–Izera Massif are represented by pyrite and magnetite deposits hosted in the Leszczyniec Unit as well as by magnetite deposit and, presumably, by a small part of tin mineralization hosted in the Izera–Kowary Unit. All these deposits and occurrences were subjected to the pre-Variscan regional metamorphism.Most of the Karkonosze–Izera Massif ore deposits and occurrences are related to the Karkonosze Granite intrusion. This group includes a spatially diversified assemblage of small ore deposits and ore mineral occurrences of: Fe, Cu, Sn, As, U, Co, Au, Ag, Pb, Ni, Bi, Zn, Sb, Se, S, Th, REE, Mo, W and Hg located within the granite and in granite-related pegmatites, in the close contact aureole of the granite and within the metamorphic envelope, at various distances from the granite. Assuming world standards, all these deposits are now uneconomic. Various age determinations indicated that ore formation connected with the Karkonosze Granite might have taken place mostly between about 326 and 270 Ma.The last ore-forming episode in the Karkonosze–Izera Massif is related to hypergenic processes, particularly important in the northern part of the massif, in the Izera–Kowary Unit where some uranium deposits and occurrences resulted from the infiltration of ore solutions that originated from the weathering of pre-existing accumulations of uranium minerals. A separate problem is the presence of oxidation zones of ore deposits and occurrences, both the fossil and the recent.A full list of ore minerals identified in described deposits and occurrences of the Karkonosze–Izera Massif together with relevant, key references is presented in the form of an appendix.     

Progress in the study and modelling of similar fold interferences

Similar fold interferences are examined in two different ways.

• 1.(1) We show the importance of taking into account the original position of the stratification with respect to the orientations of two interfering fold phases. Basin and dome cases correspond to particular orientations of the interfering phases with respect to each other. In all other cases, coaxiality may be achieved for particular positions of the original stratification.
• 2.(2) We have achieved a computer-aided modelling which allows the visualization by means of sections and block-diagrams of any two or three similar fold interferences. The program allows us to define the stratification, orientations of the various phases and their profiles (sinusoidal or drawn by hand), and orientations and dimensions of the selected section or block diagram. Faults may also be represented.This modelling method is a powerful research tool that we hope to apply in future to detailed studies of fold interferences, to achieve quantitative field models of multiply folded and faulted terranes.

     

Chemical modelling of kerogens

Models of kerogens belonging to the three classical Types have been represented at the following evolution stages:

• •-beginning of diagenesis (sensu-stricto),
• •-beginning of catagenesis,
• •-end of catagenesis.

Chemical models are drawn, using analytical data obtained on natural samples: elemental analysis, electron microscopy, ¹³C NMR, thermogravimetry, functional analysis and pyrolysis.In order both to get a statistical representation and make comparisons easier, the same molecular weight of about 25,000 has been chosen for the different models of kerogens at the beginning of the diagenesis stage.     

The 1983, M 5.9 earthquake of Heze,Shandong Province,with its short-term and imminent precursory phenomena

An earthquake (M = 5.9) occurred on November 7, 1983 in the Heze area, Shandong Province (35°17′ N, 115°17∃, H = 12 km). This earthquake belongs to the isolated type of earthquakes. There were no foreshocks; the aftershocks were few in number with their energy decreasing quickly.Within the area surrounding the main shock and up to about 200 km from the epicenter, several types of short-term and imminent anomalies were observed. The major characteristics of the anomalies are as follows:The short-term and imminent anomalies are relatively few in number. The maximum radius of the area where the anomalies occur is about 150–200 km from the epicenter. The time durations of what have been called short-term and imminent anomalies here are small, being

• 1.(1) from 10–20 days to 3–4 months and
• 2.(2) from 1–2 hours to 2–3 days, respectively. The premonitory information was scanty.

Finally, the procedure to recognize the indications of a moderate earthquake is discussed.     

Buckling loads of fully embedded vertical piles

Determination of critical buckling loads of columns in a medium which offers resistance to lateral deflections depend on:

• (a) Length of the pile, L.
• (b) Flexural stiffness of the pile, EI.
• (c) Stiffness of the soil, K, and
• (d) Boundary conditions of the pile, both at the top and the tip.

In this paper, solutions for buckling loads have been obtained in closed form by energy methods for fully embedded vertical piles for boundary conditions, pinned top-pinned tip, fixed top-fixed tip, and a linear variation of soil stiffness. The effects of pile length, soil stiffness, and boundary conditions on buckling loads and mode of buckling have been studied for pile lengths up to 24 m with EI of 477 tm², K₀ [A] from 0 to 2000 t/m² and N_h [B] from 0 to 2000 t/m³.     

Tectonoelectric zonation in the Hellenic Arc

The electrical (apparent) resistivities ρ were measured by means of the magnetotelluric effect at twenty sites in Greece and in two directions, E-W and N-S. In most of the sites, ρ_EW differs considerably from ρ_NS. These results allow the following three zones to be distinguished:

• 1.(1) an external zone along western Greece with ρ_EW >ρ_NS;
• 2.(2) an intermediate zone along the main mountain chain in continental Greece where ρ_Ns >ρ_EW and
• 3.(3) an internal zone in the northern Aegean where ρ_EW >ρ_NS.

The above resistivity zones are compared to data from geotectonic, neotectonic, seismotectonic and in situ stress measurements which all show a similar geometry of zonation almost parallel to the active Hellenic Arc.     

In situ recovery,an alternative to conventional methods of mining: Exploration,resource estimation,environmental issues,project evaluation and economics

This paper discusses the history and application of in situ recovery (ISR) to a wide variety of metals. The increasing application of ISR may provide an important method to address a key issue for the mining industry, namely the cost of production.ISR transfers a significant proportion of hydrometallurgical processing to mineralised bodies in the subsurface to directly obtain solutions of metals of interest. As a result, there is little surface disturbance and no tailings or waste rock are generated at ISR mines. However, for ISR to be successful, deposits need to be permeable (either naturally or artificially induced), and the metals of interest readily amenable to dissolution by leaching solutions in a reasonable period of time, with an acceptable consumption of leaching reagents.The paper discusses the following aspects of ISR:

• •History. ISR for uranium was introduced in 1959 in the USA, and subsequently applied in many countries over last 50 years, particularly in the USSR. The share of uranium mined by ISR reached 51% of world production in 2014, and the capacity of ISR mining of uranium is now comparable with that from conventional uranium mines.
• •Commodities. A review of the use of ISR for mining other commodities, namely copper, gold, nickel, scandium, rhenium, rare earth elements, yttrium, selenium, molybdenum, and vanadium. ISR for copper was introduced in the 1970s and there were several successful natural tests and mines. Scandium, rhenium, rare earth elements, yttrium, selenium, molybdenum, and vanadium were mined in pilot tests as by-products of uranium extraction. ISR of gold, copper, nickel, rare earth elements and scandium has been successfully developed over recent years. The paper discusses other commodities that have potential to be mined using ISR.
• •Applicability of ISR is addressed by a discussion of the features of mineralisation that need to be considered during different stages of ISR projects. Permeability,¹ hydrogeological conditions and selective leachability are the most critical parameters for ISR, and must be defined in the evaluation and exploration stages. Morphology and depth of mineralisation, thicknesses and grades, distribution of mineralisation, presence of aquicludes, and environmental conditions are also important factors for ISR projects.
• •Environmental issues. ISR allows the extraction of mineralisation with minimal disturbance to existing natural conditions. In contrast to underground and open pit mining, there are smaller volumes of mining and hydrometallurgical effluents that require management. Clearly contamination of groundwater by ISR reagents is the critical aspect requiring management during an ISR operation. Control of leaching in ISR operations and various ways of cleaning aquifers are discussed in the paper.
• •Economics. ISR operations deliver a range of benefits including lower CapEx costs for mine development, processing plant and infrastructure. ISR enables production to start at low capital cost and then a modular increase in production, as well as very flexible production capacity. The costs of ISR for different commodities (copper, gold, nickel, scandium, rhenium, rare earth elements, yttrium, selenium, molybdenum, vanadium) are discussed, with economic parameters for uranium production from ISR and conventional provided for comparison. The CapEx, OpEx and common cut-off grades for ISR for different commodities are discussed.
• •Exploration, resource estimation and the development of ISR projects require a number of different approaches compared to conventional mining projects. These criteria and the necessary methodology for resource estimation for ISR projects are described in the article.