Breccia Pipes Research Articles

The Natural Defenses of Copper Flat Sierra County, New Mexico

Copper Flat, located in southwestern New Mexico, approximately 23 miles southwest of Truth or Consequences, is a porphyry copper deposit with associated gold, silver, molybdenum, and sulfide minerals. The stock contains a 75 million-year-old quartz monzonite breccia pipe forming the center of an eroded andesite strato-volcano. Quintana Minerals Corporation mined the property for three months in 1982 producing 7.4 million pounds of copper, 2,306 ounces of gold, and 55,966 ounces of silver. Mining activities ceased because of low copper prices. The mining equipment was dismantled and sold. Since no mining activities have occurred since 1982, the site is an excellent field laboratory for studying the behavior of metals and sulfide minerals exposed with waste rock and tailings in the arid southwest. There is a 12.8-acre pit and pit lake on site that is located near the center of the breccia pipe. The entire study undertaken at Copper Flat focused on the potential impact of the pit lake, the waste rock piles, and the tailing impoundment on the local surface and groundwater quality; however, this paper focuses on the pit lake. The pit lake has been sampled at least 65 times between 1989 and 1997. The pH of the lake is typically neutral to alkaline, with exception occurring in 1992 and 1993, where the pH dropped as low as 4.4. At least one intermittent seep from the pit wall has been sampled and the results reported a pH of 2.64, a total dissolved solid concentration (TDS) of 12,770 milligrams per liter (mg/L), and a sulfate concentration of 790 mg/L. The andesitic host rocks surrounding the ore body and groundwater inflow have a high acid buffering capacity as shown by the partial dissolution of calcite and the precipitation of gypsum and goethite. The alkalinity of the groundwater and host rocks quickly neutralizes and dilutes acidic discharges into the pit lake. Groundwater samples collected from monitoring wells located down gradient from the pit lake indicate groundwater chemistry is similar before and after the excavation of the pit.

EPITHERMAL SYSTEMS AND GOLD MINERALIZATION IN WESTERN THRACE (NORTHERN GREECE)

Extensive epithermal systems occur within the Tertiary volcanosedimentary basins of western Thrace northern Greece. Gold deposits or perspective gold districts, related to the above epithermal systems have been recently found in the area. The gold mineralization is of the high – sulfidation type and is associated to a diversity in composition and style volcanic activity. Sappes epithermal system is the most important (Saint Demetrios and Viper deposits) and has developed in volcanic "ocks of intermediate composition accompanied by subvolcanic intrusives (dacite - andésites) and plutonio rocks (quartz - monzodiorites). Saint Demetrios and Viper gold deposits are flat lying and of high sulfidation type mineralizations hosted in hydrothermal breccia zones. Petrota epithermal system has developed in volcanoclastic and epiclastic rocks (Perama Hill gold deposit), in rhyolites (location Othontoto) and within hyaloclastites and crystal tuffs (location Mavrokoryfi). The mineralized epithermal zones have strong structural control. Perama gold deposit occurs at the intersection of NS and NW trending epithermal zones. These structures represent the higher grade "feeder" system. Pefka epithermal system is hosted in more acid volcanic vocks (dacites, rhyodacites) and at its southern part (Pasa lofos area) the system is associated with a more alkaline suit (shoshonitic rocks). The mineralized silicifid zones at Pefka mine would correspond to concentric fractures (sheeted fracturing) parallel to the margin of the breccia pipe. The gold mineralization occurs in veins. In general gold occurs in the form of native gold, gold tellurides or it is associated with enargite, luzonite, tetrahedhte. Advanced argillic alteration and intense silicification are very important for the epithermal systems in western Thrace. A unique low - sulfidation occurrence was found at the central and southern part of Sappes area. Adularla was found in veinlets overlapping argillic alteration zones of high - sulfidation system.

Mercury as a useful pathfinder for the Chinkuashih enargite-gold deposits, Taiwan

The Chinkuashih is a group of dacite-related hydrothermal enargite-gold deposits of the Quaternary age, which produced 94 tons of gold and 119,101 tons of copper from 1895 to 1987. It has remaining reserves of 656 tons of gold with an average grade range of 1.5–3.5 g/ton of Au for all orebodies discovered. Mercury content in different media such as stream sediments, heavy minerals in stream sediments, soils, rocks/ores, and pyrite samples was analyzed by a gold–film mercury detector to evaluate whether mercury is a good pathfinder for these types of deposits at Chinkuashih. The gold film technique is more rapid and cheaper than the traditional fire assay or fire assay/ICP-MS gold and trace element analyses. Mercury in stream sediments and soils indicated the border zone of gold mineralization 12 km away from the center of mineralization at Chinkuashih. Mercury in heavy minerals of the stream sediments distinguished the intermediate zone with gold veins and gold/gold–copper breccia pipes from the core or inner zone with the gold–copper zone. It has been found that contours of 1000 or 500 ppb Hg of soil samples can delineate the outcropping gold orebodies. The gold ores generally contain 1000 ppb or more Hg.

The development and fracturing of plutonic apexes: implications for porphyry ore deposits

Porphyry ore deposits are generally located above plutonic apexes, described as finger-like extrusions from a large underlying silicic magma chamber. Fractures and faults that concentrate around these shallow structures allow mineral-enriched hydrothermal and magmatic fluids to circulate and exchange heat and mass with the host rock. Plutonic apexes, however, are not necessarily mineralized. The physical mechanisms invoked for their development and fracturing are focused on the role of volatile pressure, and we have no clear explanation on the associated thermo-mechanical processes. Here we present (a) a semi-quantitative scenario to explain how significant relief could form at the magma chamber roof to give apexes frozen within the shallow crust, and (b) the results of our numerical modeling of fracturing at plutonic apexes. We suggest that morphologic instabilities, expressed by two-directional corrugations (crests and troughs) at the crystallizing roof of the magma chamber, could arise at the top of large silicic batholiths as a result of thermo-mechanical interactions between the reservoir and its surroundings. The corrugated roofs could form with local apexes several kilometers high. Given that a local extensional tectonic regime would surround such systems, crystallization of the apexes would promote a concentration of fractures and faults in their vicinity. In modeling the thermo-mechanical regime around a plutonic apex to show how fractures and faults could develop, we tested different values for temperature contrasts, extension rates and magma viscosity. Two main regimes can be identified, depending on the rheological contrast between the magma and its host rock: the one, a single thick fault connecting the apex to the surface (analogous to a breccia pipe), and the other a network of fractures surrounding the apex (analogous to a stockwork). Where two apexes are close together, one will cluster the shear stresses, regardless of its vertical extension, and thus only a single fracture will develop. We thus infer that barren apexes can be located near mineralized apexes if the distance between them is no greater than the thickness of the brittle layer, which in turn is highly dependent on local thermal and mechanical conditions.

Fluid overpressure in layered intrusions: formation of a breccia pipe in the Eastern Bushveld Complex, Republic of South Africa

Fluids and volatile fluid overpressures in layered intrusions are becoming recognized as having important functions in magma chamber processes for the formation of magmatic structures and for the movement and concentration of economically important ore elements. We re-examine a breccia pipe in the Bushveld Complex to investigate the role of volatile fluid overpressure in its emplacement. This 10-m-diameter breccia pipe was emplaced vertically in the anorthosite of the Upper Critical Zone of the Bushveld Complex and contains blocks of Bushveld anorthosite, norite, and pyroxenite, apparently derived from lower in the stratigraphy. The blocks are commonly elongate, and are tightly packed within an ultramafic pegmatite groundmass. Ultramafic pegmatitic dikes radiate bilaterally from the pipe. Microprobe analyses of plagioclase in the breccia pipe blocks reveal that these grains are unzoned and have higher anorthosite content (~An85) than host rock plagioclase (~An75), indicating that the breccia pipe blocks were transported considerable vertical distances. Whole-rock major- and trace-element data show enrichment in fluid-soluble incompatible elements, supporting the role of volatile fluids in the formation of the pipe. A model is examined in which the segregation of a fluid phase from interstitial liquids in the cumulate section below the breccia pipe leads to the development of sufficient overpressure for its explosive emplacement. Fluid overpressure can develop by compaction and during crystallization of plagioclase-saturated silicate liquids as fluids exsolve from the solidifying interstitial liquid. If fluids separate faster than they can escape from the crystal pile, significant overpressures can develop. The minimum fluidization velocity which would be required to emplace blocks of the size and density found within the breccia pipe is found to be 10–110 m/s. The crystallization model predicts the development of about 400 bar of overpressure, an amount calculated to be sufficient for pipe emplacement.

Exploration at the Kuscayiri Au (Cu) prospect and its implications for porphyry-related mineralization in western Turkey

The Kuscayiri Au (Cu) deposit is localized along EW-trending linear silica-quartz structures or pods within altered Lower Miocene volcanics that are underlain by medium to high level Mesozoic granodiorite intrusions. The deposit is characterized by disseminated or fracture-controlled pyrite (up to 12%), variable amounts of silicification, hematite–pyrite matrix breccias produced by intense fracturing of siliceous rocks and moderate to weak saccharoidal to crystalline quartz stringer stockwork veining in small breccia pipes. An early quartz–sericite alteration event was focused along the EW-trending structures and resulted in the precipitation of pyrite. A later, more spatially extensive, advanced argillic alteration event overprinted the quartz–sericite event. The highest gold content is restricted to the high-temperature portion of the alteration zone characterized by stockwork or replacement quartz associated with sericite–pyrite–alunite–pyrophyllite. Trace gold and associated magnetite, arsenopyrite, realgar, specular hematite and chalcopyrite also occur within the smectite–illite/smectite–kaolinite–chlorite alteration facies. During the Tertiary, widespread subaerial to subaqueous arc volcanism developed in western Turkey, and numerous occurrences of high/low sulfidation epithermal systems are associated with major NW–SE extensional deformation. The resultant NE–SW-trending grabens appear to be highly favorable host environments for the formation of porphyry-related gold–copper systems. The Kuscayiri mineralization may represent a lithocap with Au (Cu), the top of one such system yet to be discovered.

Karst in evaporite rocks of the United States

Evaporites are the most soluble of common rocks; they are dissolved readily to form the same range of karst features that typically are found in limestones and dolomites. Evaporites, including gypsum (or anhydrite) and salt, are present in 32 of the 48 contiguous United States, and they underlie about 35–40% of the land area. Evaporite outcrops typically contain sinkholes, caves, disappearing streams, and springs. Other evidence of active karst in evaporites includes surface-collapse features and saline springs or saline plumes that result from dissolution of salt. Many evaporites, including some in the deeper subsurface, also contain evidence of paleokarst that is no longer active; this evidence includes dissolution breccias, breccia pipes, slumped beds, and collapse structures. Evaporites occur in 24 separate structural basins or geographic districts in the United States, and either local or extensive evaporite karst is known in almost all of these basins or districts. Human activities also have caused development of evaporite karst, primarily in salt deposits. Boreholes or underground mines may enable (either intentionally or inadvertently) unsaturated water to flow through or against salt deposits, thus allowing development of small to large dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures can cause land subsidence or catastrophic collapse. Evaporite karst, both natural and human-induced, is far more prevalent than commonly believed.

McCauley Sinks: A compound breccia pipe in evaporite karst, Holbrook basin, Arizona, U.S.A.

The McCauley Sinks, in the Holbrook basin of northeastern Arizona, are comprised of some 50 individual sinkholes within a 3-km-wide depression. The sinks are grouped in a semi-concentric pattern of three nested rings. The outerring is an apparent tension zone containing ring fractures. The two innerrings are semi-circular chains of large sinkholes, ranging up to 100m across and 50m deep. Severalsub-basins within the larger depression show local downwarping and possible incipent sinkholes.

Environmental problems caused by gypsum karst and salt karst in Great Britain

In Great Britain, gypsum karst is widespread in the Late Permian (Zechstein) gypsum of north-eastern England. Here and offshore, a well-developed palacokarst with large breccia pipes was formed by dissolution of the underlying Permian gypsum. Farther south, around Ripon, the same rocks are still being dissolved, forming an actively evolving phreatic gypsum-maze cave system. This is indicated by the presence of numerous active subsidence hollows and sulphate-rich springs. In the English Midlands, gypsum karst is locally developed in the Triassic deposits south of Derby and Nottingham. Where gypsum is present, its fast rate of dissolution and the collapse of overlying strata lead to difficult civil-engineering and construction conditions; these can be further aggravated by water abstraction. Salt (halite) occurs within British Permian and Triassic strata, and has a long history of exploitation. The main salt fields are in central England and the coastal areas of northwest and northeast England. In central England, saline springs indicate that rapid, active dissolution occurs that can cause subsidence problems. In the past, subsidence was aggravated by shallow mining and the uncontrolled extraction of vast amounts of brine. This has now almost stopped, but there is a legacy of unstable buried salt karst, formed by both natural and induced dissolution. The buried salt karst occurs at depths ranging from about 40 m to 130 m; above these depths, the overlying strata are foundered and brecciated. In the salt areas, construction and development are hampered by both abandoned mines and by natural or induced brine runs, with their associated unstable ground.

The Donoso copper-rich, tourmaline-bearing breccia pipe in central Chile: petrologic, fluid inclusion and stable isotope evidence for an origin from magmatic fluids

The copper-rich, tourmaline-bearing Donoso breccia pipe is one among more than 15 different mineralized breccias in the giant (>50 million metric tonnes of copper) Miocene and Pliocene Rio Blanco-Los Bronces copper deposit in the high Andes of central Chile. This breccia pipe, bracketed in age between 5.2 and 4.9 Ma, has dimensions of 500 by 700 m at the current surface 3,670 m above sea level. Its roots have yet to be encountered, and it is >300 m in diameter at the depth of the deepest drill holes. The Donoso breccia is, for the most part, monolithic, containing clasts of the equigranular quartz monzonite pluton which hosts the pipe. It is matrix supported, with between 5 and 25% of the total rock volume consisting of breccia-matrix minerals, which include tourmaline, quartz, chalcopyrite, pyrite, specularite, and lesser amounts of bornite and anhydrite. An open pit mine, centered on this breccia pipe, has a current production of 50,000 tonnes of ore per day at an average grade of 1.2% copper, and copper grade in the breccia matrix is significantly higher. Measured δ18O for tourmaline and quartz from the matrix of the Donoso breccia at different levels of the pipe range from +6.9 to +12.0‰, and measured δD in tourmaline ranges from –73 to –95‰. Temperatures of crystallization of these minerals, as determined by the highest homogenization temperatures of highly saline fluid inclusions, range from 400 to >690°C. When corrected for these temperatures, the stable isotope data indicate that fluids from which these breccia-matrix minerals precipitated were magmatic, with δ18O between +5.6 to +9.1‰ and δD between –51 to –80‰. These isotopic data preclude participation of a significant amount of meteoric water in the formation of the Donoso breccia. They support a model in which brecciation is caused by expansion of magmatic fluids exsolved from a cooling pluton, and breccia-matrix minerals, including copper sulfides, precipitated from the same magmatic fluids responsible for brecciation. Sericitic alteration of clasts in the breccia was also caused by these magmatic fluids. Different types of fluid inclusions imply that several different magmatic fluids were involved in formation of the Donoso breccia. These include high-temperature, highly saline, non-boiling fluids, trapped in inclusions that homogenize by halite dissolution, which probably exsolved from a magma cooling under relatively high (>1 kbar) lithostatic pressure conditions, consistent with geologic constraints. Other high-temperature, highly saline fluids are trapped in inclusions that homogenize by vapor-bubble disappearance and are spatially associated with vapor-rich inclusions, suggesting either phase separation (boiling) or simultaneous separation of immiscible brine and vapor from a magma cooling at lower hydrostatic pressure conditions. Both types of high-temperature, highly saline fluids circulated intermittently, as pressure fluctuated between lithostatic and hydrostatic conditions because of episodes of sealing and rebrecciation.

The Port Mouton Shear Zone: intersection of a regional fault with a crystallizing granitoid pluton

The peraluminous tonalite–monzogranite Port Mouton Pluton is a petrological, geochemical, structural, and geochronological anomaly among the many Late Devonian granitoid intrusions of the Meguma Lithotectonic Zone of southern Nova Scotia. The most remarkable structural feature of this pluton is a 4-km-wide zone of strongly foliated (040/subvertical) monzogranites culminating in a narrow (10–30 m), straight, zone of compositionally banded rocks that extends for at least 3 km along strike. The banded monzogranites consist of alternating melanocratic and leucocratic compositions that are complementary to the overall composition of that part of the pluton, suggesting an origin by mineral–melt and mineral–mineral sorting. Biotite and feldspar are strongly foliated in the plane of the compositional bands. These compositional variations and foliations originated by a process of segregation flow during shearing of the main magma with a crystallinity of 55–75%. Subsequent minor brittle fracturing of feldspars, twinning of microcline, development of blocky sub-grains in quartz, and kinking of micas demonstrate overprinting by a high-temperature deformation straddling the monzogranite solidus. Small folds and late sigmoidal dykes indicate dextral movement on the shear zone. This Port Mouton Shear Zone (PMSZ) is approximately co-linear with the only outcrops of Late Devonian mafic intrusions in the area, two of which are syn-plutonic with well-developed mingling textures in the marginal tonalite of the Port Mouton Pluton. Also closely co-linear with the mafic intrusions are a granitoid dyke that extends well beyond the outer contact of the Port Mouton Pluton, a swarm of large aligned angular xenolithic slabs, a zone of thin wispy schlieren banding, a large Be-bearing pegmatite, and a breccia pipe with abundant garnetiferous metapelitic xenoliths. In various ways, the shear zone may control all of these features. The Port Mouton Shear Zone is parallel to many other NE-trending faults and shear zones in the northern Appalachians, probably related to the docking of the Meguma Zone along the Cobequid–Chedabucto Fault system.

Some metallogenic features of gold and copper deposits related to alkaline rocks and consequences for exploration

Porphyry copper-gold, skarn copper-gold, sediment-hosted (Carlin-style) gold, breccia pipe, low-sulphidation epithermal gold, pluton-related (mesothermal or orogenic) gold vein and volcanogenic massive sulphide deposits associated with alkaline rocks are commonly broadly similar to those hosted by their calc-alkaline counterparts. In contrast, porphyry molybdenum-gold deposits are confined to alkaline igneous centres. Alkaline suites are notably deficient in high-sulphidation epithermal gold deposits and even in the advanced argillic lithocaps which host them. This is surprising, given that the required oxidised sulphur species are seemingly more abundant than in calc-alkaline igneous centres. Highly efficient buffering of acidic fluid by metasomatised alkaline rocks may offer a viable explanation. All types of intrusion-related zinc deposits also appear to be poorly developed in alkaline provinces. The characteristics of several gold and copper deposits associated with alkaline rocks, including the giant Porgera, Cripple Creek, Ladolam, Olympic Dam and Phalaborwa examples, are judged to diverge appreciably from their most closely related deposit types, rendering them arguably unique. Most of these aberrant mineralisation styles may be due to variations in magmatic-fluid compositional and liberation characteristics consequent upon the extreme diversity of ore-related alkaline magmas. Most types of gold and copper deposits developed in calc-alkaline provinces also constitute exploration targets in and around alkaline igneous centres, although porphyry copper-gold and low-sulphidation epithermal gold deposits are considered to possess the greatest potential. Perhaps of even greater interest, however, is the possibility of encountering unconventional giant gold and copper deposits which lack closely analogous examples. If already-defined aberrant deposits are truly unique, then exploration designed specifically to detect additional examples is pointless. Furthermore, exploration for new unique deposits is difficult because their defining geological parameters are unknown. Alkaline rocks within or behind calc-alkaline arcs at convergent plate boundaries probably offer the greatest exploration potential, although anorogenic intracontinental extensional settings should not be ignored.

Gold deposits in the Xiaoqinling-Xiong'ershan region, Qinling Mountains, central China

The gold-rich Xiaoqinling–Xiong'ershan region in eastern Shaanxi and western Henan provinces, central China, lies about 30–50 km inland of the southern margin of the North China craton. More than 100 gold deposits and occurrences are concentrated in the Xiaoqinling (west), Xiaoshan (middle), and Xiong'ershan (east) areas. Late Archean gneiss of the Taihua Group, and Middle Proterozoic metavolcanic rocks of the Xiong'er Group are the main host rocks for the deposits. Mesozoic granitoids (ca. 178–104 Ma) are present in most gold districts, but deposits are typically hosted in the Precambrian basement rocks hundreds of meters to as far as 10 km from the intrusions and related hornfels zones. Deposits in the Xiaoqinling and Xiaoshan areas are best classified as orogenic gold deposits, with ores occurring in a number of distinct belts both in quartz veins and disseminated in altered metamorphic rocks. Alteration assemblages are dominated by quartz, sericite, pyrite, and carbonate minerals. The ore-forming fluids were low salinity, CO2-rich, and characterized by isotopically heavy δ18O. Four deposits (Dongchuang, Wenyu, Yangzhaiyu, and Dahu) in the Xiaoqinling area each contain resources of about 1 Moz Au. Some of the gold deposits in the Xiong'ershan area represent more shallowly emplaced tellurium-enriched orogenic systems, which include resources of approximately 1–1.5 Moz Au at Shanggong and Beiling (or Tantou). Others are epithermal deposits (e.g., Qiyugou and Dianfang) that are hosted in volcanic breccia pipes. Isotopic dates for all gold deposits, although often contradictory, generally cluster between 172–99 Ma and are coeval with emplacement of the post-kinematic granitoids. The gold deposits formed during a period of relaxation of far-field compressional stresses, clearly subsequent to the extensive Paleozoic–early Mesozoic accretion of arc terranes and the Yangtze craton onto the southern margin of the North China craton. Hydrothermal and magmatic events occurred locally where extension-related Precambrian basement uplifting took place along the craton margin. Fluids for the orogenic gold deposits in the Xiaoqinling, Xiaoshan, and Xiong'ershan areas may have been released from evolving magmas or resulted from prograde metamorphic reactions within the uplift zones. Alternatively, for the epithermal gold deposits at shallower levels in the Xiong'ershan area, gold-transporting fluids were mainly exsolved from coeval magmas, although meteoric water was also involved in these hydrothermal systems.

Erratum to A new style of Ni-Cu mineralization related to magmatic breccia pipes in a transpressional magmatic arc, Aguablanca, Spain

The Aguablanca deposit represents a new style of magmatic Ni-Cu mineralization in discordant sulfide-rich pyroxenitic breccia pipes. The orebody is hosted by Variscan calc-alkaline diorites and gabbros which intruded during an oblique subduction/collision event. Transpressional-transtensional left-lateral structures facilitated the intrusion of primitive magmas to shallow depths in the crust. A two-stage genetic model is proposed. In the first stage, a transitional deep magma chamber formed. The primitive magma interacted at depth with wall rocks, resulting in extensive crustal contamination, concomitant sulfide magma immiscibility and settling of orthopyroxene-, clinopyroxene- and sulfide-rich cumulates to form a layered magmatic complex. Geochemical and mineralogical evidence, including the virtual disappearance of olivine, heavy 34S values (7.4‰), distinctive Nd, Sr and Pb signatures, high Au contents, and the presence of spinel and graphite indicate a major interaction with the upper crust, probably with pyrite-rich carbonaceous slates of Late-Proterozoic age. The second stage was related with the emplacement of residual calc-alkaline gabbroic to noritic melts and the development of an intrusive breccia containing fragments of the consolidated layered complex rocks and associated disseminated to massive sulfides.

A new style of Ni-Cu mineralization related to magmatic breccia pipes in a transpressional magmatic arc, Aguablanca, Spain

A new style of Ni-Cu mineralization related to magmatic breccia pipes in a transpressional magmatic arc, Aguablanca, Spain

Historical, Geological, and Mining Benchmarks Concerning the Endogeneous Breccia Structures Associated with the Neogene Magmatic Events in Romania (in Romanian)

An up-to date exhaustive bibliographic study is presented in order to highlight the evolution of the knowledge of endogenous breccias related to Neogene magmatism from Romania during the 19th and 20th centuries. This approach is based mainly on Romanian literature but there are also several foreign citations. Instead of the general opinion (widespread among Romanian mining companies) according to which the occurrence of the breccia structures in Romania is scarcely, this paper show the ubiquitous presence of breccia pipe and breccia dyke structures among the Neogene ore deposits from Romania, in Apuseni Mountains as well as in Eastern Carpathians.

Oxygen and Carbon Isotope Study of Calcite and Dolomite in the Disseminated Au‐Ag Telluride Bulawan Deposit, Negros Island, Philippines

Abstract: The disseminated Au‐Ag telluride Bulawan deposit, Negros island, Philippines, is hosted by dacite porphyry breccia pipes which formed in a Middle Miocene dacite porphyry stock. Electrum and Au‐Ag tellurides occur mostly as grains intergrown with or filling voids between sphalerite, pyrite, chalcopyrite, galena and tennantite. Calcite, quartz and rare dolomite are the principal gangue minerals. Four types of alteration were recognized in the deposit, namely; propylitic, K‐feldspar‐sericitic, sericitic and carbonate alteration. Carbonate alteration is correlatable to the gold deposition stage and occurs mostly along fault zones.The δ18O and δ13C compositions of calcite and dolomite in propylite zone and ore‐stage dacite porphyry breccia were determined. The δ18O values of calcite in propylitized andesite range from +12.2 to +14.7%, and their δ13C values range from ‐6.1 to ‐1.0%. The δ18O values of calcite and dolomite in sericite‐ and carbonate‐altered, mineralized dacite porphyry breccia and dacite porphyry rocks range from +15.1 to +23.1%, and the δ13C values of calcite and dolomite range from ‐3.9 to +0.9%. The δ18O and δ13C values of the hydrothermal fluids were estimated from inferred temperatures of formation on the basis of fluid inclusion microthermometry. The δ18O values of hydrothermal fluid for the propylitic alteration were calculated to be +8.5 ‐ +9.5%, assuming 375°C. On the other hand, the δ18O values of ore solutions for base metal and Au mineralization were computed to be +13.6 ‐ +14.6%, assuming 270°C. The hydrothermal fluids that formed the Bulawan deposit are dilute and 18O‐enriched fluids which reacted with 18O‐ and 13C‐rich wallrocks such as limestone.

The Phalabowra (Palabora) carbonatite-hosted magnetite-copper sulfide deposit, South Africa: an end-member of the iron-oxide copper-gold-rare earth element deposit group?

Olympic Dam-type iron-oxide copper–gold deposits are widely recognised in terrains with significant Palaeoproterozoic to Mesoproterozoic granitic magmatism. Most researchers favour a magmatic association for these deposits, but none of the 100–2000 Mt recognised copper-bearing deposits has a spatial and/or temporal relationship to an intrusive body of sufficient dimensions to produce the hosting giant breccia and/or hydrothermal systems. In other words, if the recognised ore-bodies are magmatic-hydrothermal, they must be classified as distal deposits. The magnetite–copper–phosphate–rare earth element pipe-like carbonatite-hosted orebody at Loolekop, within the larger Phalabowra Carbonatite Complex, has many features to suggest that it represents an end member of the Olympic Dam-type deposit class hosted within its magmatic source rock. It (1) falls broadly within the appropriate age range, (2) has a similar giant size and low copper grade, (3) is dominated by magnetite, (4) has sulfur-poor copper-sulfide minerals and lacks iron sulfides, (5) is silica-poor, and (6) is enriched in REE, particularly LREE, as well as P, F, U and Th. As an end member of the Olympic Dam-type deposits, the Loolekop orebody can help explain the common siting of the deposits at craton edges or other lithospheric boundaries, where decompression melting of metasomatised mantle can produce volatile-rich alkaline melts (rich in REE, P, F, etc.). Such melts are capable of generating sulfur-deficient volatiles enriched in copper and gold, among other elements, as well as phreatic breccia pipes and associated intense metasomatism, the most common features of the Olympic Dam-type deposits.

Time-Domain Spectral IP and Its Applications in the Southern Chinkuashih Area, Northern Taiwan

The IP measurement has a low background value above which IP data can be called anomalous, yielding a more definitive interpretation than other geophysical methods. For resolving IP sources, broad band IP data should be collected. The most cost effective way to obtain enough spectral IP (SIP) information routinely is by time-domain SIP measurement. Although the Cole-Cole parameters (chargeability M, time const T and exponent c) have been found to be very useful in resolving SIP sources in a frequency-domain, these parameters can also be determined through computer matching of the time-domain SIP data by the best fit in a family of pre-calculated Cole-Cole curves. Time-domain SIP has first been applied to the southern Chinkushih area, northern Taiwan, for the resolution of SIP sources. Based on the time domain SIP analysis, possible concealed porphyry gold/copper deposits, or breccia pipes in the margin of the Wutanshan intrusion were located.

Occurrence of mining-induced open fissures and shear walls in the Permian limestones of County Durham

Subsidence-induced fissures and vertical relative movements in the Permian limestones of County Durham, England, are locally familiar, but poorly documented phenomena. They result from block rotation within the limestone rock mass as stress relief opens previously closed joints and faults in the relatively strong limestone following subsidence in the underlying weak, unconformable Coal Measures strata during and after mining operations. This creates patterns of surface subsidence that are not well described in the subsidence literature and which represent a potential hazard to leisure activities, construction, quarrying and agriculture.Four main subsidence features dominate the surface topography, each with its own associated unique hazard. These surface features are: large, deep open fissures; small open fissures; shear cliff walls; and fault breccia pipe collapse. All new developments on Permian strata should be the subject of in-depth mining reports carried out with reference to these features. In practice it is possible to predict where all these features may occur. Large, deep open fissures and, where traceable, small open fissures should be dug out, and where development work is being undertaken on ground that may be susceptible to small open fissures impermeable barriers should be considered in the foundation design to mitigate possible gas migration.