Mantos Blancos Research Articles

An Alternative Technology to Obtain Dewatered Mine Tailings: Safe and Control Environmental Management of Filtered and Thickened Copper Mine Tailings in Chile

An alternative process to obtain a high degree of dewatering tailings that produces a high-density product is presented in this article. This technology involves the combination of tailings particle grain size classification by hydrocyclones (HC) and tailings dewatering by horizontal vibratory screens (HVS). It makes it possible to dewater tailings to a high grade of performance. This alternative technology (HC-HVS) involves the recovery of water from the coarse fraction of tailings (sands) through two hydrocycloning stages, followed by a dewatering stage of cycloned tailings sands on horizontal vibratory screens, to reduce moisture content and turn it into a “cake”. The resulting coarse fraction tailings are easily transported to a dry stack tailings storage facility (TSF). The fine fraction of tailings (slimes) can be dewatered on thickener equipment to recover part of the process water. Finally, this article describes the main benefits of this alternative dewatered tailings technology with an emphasis on (i) dewatering technology evolution over the last 17 years; (ii) process stages features; (iii) pilot test results; (iv) tailings properties analysis (such as particle grain size distribution, fines content) and (v) lessons learned about the experience gained in the operation of Mantos Blancos case study with dry stack tailings storage facility.

"Invisible" silver in chalcopyrite and bornite from the Mantos Blancos Cu deposit, northern Chile

Relatively little is known about the mineralogical occurrence and geochemical controls on the incorporation of “invisible” (refractory) silver and gold in hydrothermal sulfide minerals. Secondary ion mass spectrometry (SIMS) analysis reveals that bornite (81–649 ppm Ag) and chalcopyrite (0.61–2211 ppm Ag) are major hosts for silver in the Mantos Blancos deposit (500 Mt, @1 wt% Cu), the largest Jurassic stratabound Cu-(±Ag) deposit in the Costal Range of northern Chile. Gold concentrations are generally two orders of magnitude lower, ranging from 0.05 to 1.66 ppm Au in chalcopyrite, and 0.08 to 2.38 ppm Au in bornite. In addition to precious metals, SIMS analysis shows significant concentrations of As (~100 ppm in chalcopyrite, <10 ppm in bornite), whereas other metalloids and chalcogens, such as Sb, Se, and Te, have highly variable concentrations ranging from tens of ppb to ppm levels. These microanalytical results are consistent with a two-stage hydrothermal evolution model, as recently proposed for the Mantos Blancos deposit. Within this context, Ag, Au, As, and base metals were most likely sourced from a Late Jurassic (~155 Ma) rhyolitic dome, and partitioned into bornite and chalcopyrite in quartz-sericite veins after cooling below ~430°C. This first hypogene Cu-Ag ± Au event was followed by a second, higher-temperature alteration phase (400–600 °C) related to the emplacement of diorite and granodiorite stocks (~141–152 Ma), in which Ag and Au were partitioned into fine-grained, porous chalcopyrite in potassic alteration vein assemblages. When coupled with recent studies in the area, results presented here confirm that the high Ag endowment of Mantos Blancos is the result of multiple pulses of hypogene mineralization followed by supergene enrichment of metals.

Supergene enrichment of copper deposits since the onset of modern hyperaridity in the Atacama Desert, Chile

Supergene enrichment of Cu deposits in the Atacama Desert has played a critical role in making this the prime Cu-producing province of the world. Previously, this has been believed to have occurred exclusively over a long period from the middle Eocene to the late Miocene, which ended when climatic conditions changed from arid to hyperarid. Here, we report U-series disequilibrium ages in atacamite-bearing supergene assemblages that provide a new conceptualization on both the supergene enrichment process and the onset of extreme hyperaridity in the Atacama Desert. 230Th–234U ages of gypsum intergrown with atacamite in supergene veins from Cu deposits cluster at ~240 ka (Chuquicamata), 130 ka (Mantos Blancos, Spence), and 80 ka (Mantos de la Luna, Michilla). When coupled with previous data, these results indicate that supergene enrichment of Cu deposits did not cease after the onset of hyperaridity. We propose that supergene enrichment in the Atacama region developed in two main stages. The main phase, caused by downward circulation of meteoric waters in a semi-arid setting, was active from 45 until ~9 Ma, with a last pulse ca. 5 Ma in the southern Atacama Desert. During this phase, atacamite-bearing supergene assemblages were not preserved because atacamite requires saline water for its formation and rapidly dissolves when contacted by meteoric water. This was followed by a second stage starting at ~2–1.5 Ma and continuing until at least the late Pleistocene, when deep formation waters derived from the basement passed up through and modified the pre-existing supergene Cu oxide minerals. Atacamite has then been preserved in the prevailing hyperarid climate.

Atacamite formation by deep saline waters in copper deposits from the Atacama Desert, Chile: evidence from fluid inclusions, groundwater geochemistry, TEM, and 36Cl data

The presence of large amounts of atacamite in oxide zones from ore deposits in the Atacama Desert of northern Chile requires saline solutions for its formation and hyperarid climate conditions for its preservation. We investigated the nature and origin of atacamite-forming solutions by means of coupling groundwater geochemical analyses with fluid inclusion data, high-resolution mineralogical observations, and chlorine-36 (36Cl) data in atacamite from the Mantos Blancos and Spence Cu deposits. In both deposits, the salinities of fluid inclusions in atacamite are comparable to those measured in saline groundwaters sampled from drill holes. The average salinity of fluid inclusions in atacamite for the Mantos Blancos and Spence deposits (~7–9 and 2–3 wt.% NaCleq, respectively) are strongly correlated to the salinities at which gypsum supersaturates from groundwaters in both deposits (total dissolved solids ~5–9 and 1–3 wt.% NaCleq, respectively). This correlation is confirmed by transmission electron microscopy observations of atacamite-bearing samples, revealing an intimate association between atacamite and gypsum that can be traced down to the nanometer scale. 36Cl data in atacamite provide new lines of evidence concerning the origin and age of the saline waters that formed atacamite in various stratabound and porphyry Cu deposits from the Atacama Desert. All atacamite samples show very low 36Cl-to-Cl ratios (11 × 10−15 to 28 × 10−15 at at−1), comparable to previously reported 36Cl-to-Cl ratios of deep formation waters and old groundwaters. In addition, 36Cl-to-Cl ratios in atacamite correlate with U and Th concentration in the host rocks but are independent from distance to the ocean. This trend supports an interpretation of the low 36Cl-to-Cl ratios in atacamite as representing subsurface production of fissiogenic 36Cl in secular equilibrium with the solutions involved in atacamite formation. Therefore, 36Cl in atacamite strongly suggest that the chlorine in saline waters related to atacamite formation is old (>1.5 Ma) but that atacamite formation occurred more recently (<1.5 Ma) than suggested in previous interpretations. Our data provide new constraints on the origin of atacamite in Cu deposits from the Atacama Desert and support the recent notion that the formation of atacamite in hyperarid climates such as the Atacama Desert is an ongoing process that has occurred intermittently since the onset of hyperaridity.

Magmatic evolution of the Mantos Blancos copper deposit, Coastal Range of northern Chile: insight from Sr–Nd isotope, geochemical data and silicate melt inclusions

AbstractThe Mantos Blancos copper deposit (500 Mt at 1.0% Cu) was affected by two superimposed hydrothermal events: (i) phyllic alteration related to a rhyolitic dome emplacement and brecciation at ca 155 Ma; and (ii) potassic, sodic and propylitic alteration at ca 142 Ma, coeval with stocks and sills emplacement of dioritic and granodioritic porphyries, that locally grade upwards into polymictic magmatic hydrothermal breccias. Major hypogene copper sulfide mineralization is related to the second event. A late‐ore mafic dike swarm cross‐cuts all rocks in the deposit. Two types of granodioritic porphyries can be distinguished from petrographic observations and geochemical data: granodiorite porphyry I (GP I) and granodiorite porphyry II (GP II), which resulted from two different trends of magmatic evolution. The concave shape of the rare earth element (REE) distribution pattern together with the weak or absence of negative Eu anomalies in mafic dikes, dioritic and GP I porphyries, suggest hornblende‐dominated fractionation for this magmatic suite. In contrast, distinct negative Eu anomalies and the flat REE patterns suggest plagioclase‐dominated fractionation, at low oxygen fugacity, for the GP II porphyry suite. But shallow mixing and mingling between silicic and dioritic melts are also likely for the formation of the GP II and polymictic breccias, respectively. Sr‐Nd isotopic compositions suggest that the rhyolitic dome rocks were generated from a dominantly crustal source, while the GP I has mantle affinity. The composition of melt inclusions (MI) in quartz crystals from the rhyolitic dome is similar to the bulk composition of their host rock. The MI analyzed in quartz from GP II and in the polymictic magmatic hydrothermal breccia of the deposit are compositionally more evolved than their host rocks. Field, geochemical and petrographic data provided here point to dioritic and siliceous melt interaction as an inducing mechanism for the release of hydrothermal fluids to form the Cu mineralization.

The development and application of a wind erosion model for the assessment of fugitive dust emissions from mine tailings dumps

The wind erosion of mine tailings is an air pollution concern that has not been investigated thoroughly. Indeed, there is no accurate method to predict fugitive dust emission strength of tailings dumps. This paper reports on the development of a wind erosion model based on the principles of physics. Unlike most wind erosion models developed for agricultural lands or sand dunes, this model takes into account the fluctuations in wind velocity. The model was designed to predict hourly dust emission rate of flat tailings dumps prone to wind erosion for air quality modelling purposes. The model was evaluated using wind tunnel data and field experiments which confirmed the validity of the model for crushed industrial materials. The model was further validated with field experiments undertaken by the authors at the Mantos Blancos mine in Chile.

Detailed 40Ar/39Ar dating of geologic events associated with the Mantos Blancos copper deposit, northern Chile

The 40Ar/39Ar geochronological method was applied to date magmatic and hydrothermal alteration events in the Mantos Blancos mining district in the Coastal Cordillera of northern Chile, allowing the distinction of two separate mineralization events. The Late Jurassic Mantos Blancos orebody, hosted in Jurassic volcanic rocks, is a magmatic-hydrothermal breccia-style Cu deposit. Two superimposed mineralization events have been recently proposed. The first event is accompanied by a phyllic hydrothermal alteration affecting a rhyolitic dome. The second mineralization event is related to the intrusion of bimodal stocks and sills inside the deposit. Because of the superposition of several magmatic and hydrothermal events, the obtained 40Ar/39Ar age data are complex; however, with a careful interpretation of the age spectra, it is possible to detect complex histories of successive emplacement, alteration, mineralization, and thermal resetting. The extrusion of Jurassic basic to intermediate volcanic rocks of the La Negra Formation is dated at 156.3 ± 1.4 Ma (2σ) using plagioclase from an andesitic lava flow. The first mineralization event and associated phyllic alteration affecting the rhyolitic dome occurred around 155–156 Ma. A younger bimodal intrusive event, supposed to be equivalent to the bimodal stock and sill system inside the deposit, is probably responsible for the second mineralization event dated at ca. 142 Ma. Other low-temperature alteration events have been dated on sericitized plagioclase at ca. 145–146, 125, and 101 Ma. This is the first time that two distinct mineralization events have been documented from radiometric data for a copper deposit in the metallogenic belt of the Coastal Cordillera of northern Chile.

The role of the Antofagasta–Calama Lineament in ore deposit deformation in the Andes of northern Chile

During the Late Jurassic–Early Oligocene interval, widespread hydrothermal copper mineralization events occurred in association with the geological evolution of the southern segment of the central Andes, giving rise to four NS-trending metallogenic belts of eastward-decreasing age: Late Jurassic, Early Cretaceous, Late Paleocene–Early Eocene, and Late Eocene–Early Oligocene. The Antofagasta–Calama Lineament (ACL) consists of an important dextral strike-slip NE-trending fault system. Deformation along the ACL system is evidenced by a right-lateral displacement of the Late Paleocene–Early Eocene metallogenic belts. Furthermore, clockwise rotation of the Early Cretaceous Mantos Blancos copper deposit and the Late Paleocene Lomas Bayas porphyry copper occurred. In the Late Eocene–Early Oligocene metallogenic belt, a sigmoidal deflection and a clockwise rotation is observed in the ACL. The ACL is thought to have controlled the emplacement of Early Oligocene porphyry copper deposits (34–37 Ma; Toki, Genoveva, Quetena, and Opache), whereas it deflected the Late Eocene porphyry copper belt (41–44 Ma; Esperanza, Telegrafo, Centinela, and Polo Sur ore deposits). These observations suggest that right-lateral displacement of the ACL was active during the Early Oligocene. We propose that the described structural features need to be considered in future exploration programs within this extensively gravel-covered region of northern Chile.

The Early Andean Magmatic Province (EAMP): 40Ar/ 39Ar dating on Mesozoic volcanic and plutonic rocks from the Coastal Cordillera, northern Chile

The Early Andean Magmatic Province (EAMP), consists of about 150 000 km 3 of volcanic and plutonic units in the Coastal Cordillera of northern Chile and southern Peru and represents a major magmatic Mesozoic event in the world, for which the precise age of the thick volcanic series was unknown. Thirty 40Ar/ 39Ar analyses were carried out on primary mineral phases of volcanic and plutonic rocks from northern Chile (18°30′–24°S). Reliable plateau and “mini plateau” ages were obtained on plagioclase, amphibole and biotite from volcanic and plutonic rocks, despite widespread strong alteration degree. In the Arica, Tocopilla and Antofagasta (700 km apart) regions, the ages obtained on lava flows constrain the volcanic activity between 164 and 150 Ma and no N–S migration of volcanism is observed. The uppermost lava flows of the volcanic sequence at the type locality of the La Negra Formation extruded at ca. 153–150 Ma, suggesting the end of the volcanic activity of the arc at that time. The oldest volcanic activity occurred probably at ca. 175–170 Ma in the Iquique area, although no plateau age could be obtained. The plutonic bodies of the same regions were dated between ca. 160 and 142 Ma, indicating that they were partly contemporaneous with the volcanic activity. At least one volcanic pulse around 160 Ma is evidenced over the entire investigated reach of the EAMP, according to the ages found in Arica, Tocopilla, Michilla and Mantos Blancos regions. The episodic emplacement of huge amounts of subduction related volcanism is observed throughout the whole Andean history and particularly during the Jurassic (southern Peru, northern Chile and southern Argentina). These events probably correspond to periodic extensional geodynamic episodes, as a consequence of particular subduction conditions, such as change of obliquity of the convergence, change in the subduction angle, slab roll back effect or lower convergence rate, that remain to be precisely defined.

The Mantos Blancos copper deposit: an upper Jurassic breccia-style hydrothermal system in the Coastal Range of Northern Chile

The Upper Jurassic Mantos Blancos copper deposit (500 Mt at 1.0% Cu), located in the Coastal Range of northern Chile, displays two superimposed hydrothermal events. An older phyllic alteration probably related to felsic magmatic–hydrothermal brecciation at ∼155 Ma, and younger (141–142 Ma) potassic, propylitic, and sodic alterations, coeval with dioritic and granodioritic stocks and sills, and dioritic dikes. Main ore formation is genetically related to the second hydrothermal event, and consists of hydrothermal breccias, disseminations and stockwork-style mineralization, associated with sodic alteration. Hypogene sulfide assemblages show distinctive vertical and lateral zoning, centered on magmatic and hydrothermal breccia bodies, which constitute the feeders to mineralization. A barren pyrite root zone is overlain by pyrite-chalcopyrite, and followed upwards and laterally by chalcopyrite-digenite or chalcopyrite-bornite. The assemblage digenite–supergene chalcocite characterizes the central portions of high-grade mineralization in the breccia bodies. Fluid inclusions show evidence of boiling during the potassic and sodic alteration events, which occurred at temperatures around 450–460°C and 350–410°C, and salinities between 3–53 and 13–45 wt% NaCl eq., respectively. The hydrothermal events occurred during episodic decompression due to fluid overpressuring, hydrofracturing, and sharp changes from lithostatic to hydrostatic conditions. Sulfur isotope results of hypogene sulfide minerals fall in a narrow range around 0 per mil, suggesting a dominance of magmatic sulfur. Carbon and oxygen isotopic data of calcites from propylitic alteration suggest a mantle-derived carbon and oxygen isotope fractionation due to low-temperature alteration.

A SULFUR, CARBON, OXYGEN, AND STRONTIUM ISOTOPE STUDY OF THEVOLCANIC-HOSTED EL SOLDADO MANTO-TYPE COPPER DEPOSIT, CHILE: THE ESSENTIAL ROLEOF BACTERIA AND PETROLEUM

Strata-bound, manto-type copper deposits of Chile are a major source of copper, and some deposits (e.g., Mantos Blancos, El Soldado) contain as much metal as do large porphyry copper deposits elsewhere. El Soldado (200 Mt @ 1.35% Cu), the largest manto-type copper deposit in the Coastal Cordillera of central Chile, is hosted by the rhyodacite-basalt upper member of the marine Lower Cretaceous Lo Prado Formation. Paragenetic studies indicate that the deposit formed in two stages. The first was a low-temperature stage (stage 1; 130–125 Ma) in which liquid petroleum migrated from underlying carbonaceous shales into the overlying host volcanic rocks and abundant framboidal pyrite developed in a paleopetroleum reservoir. A later hydrothermal stage (stage 2; ca. 103 Ma) introduced copper and replaced earlier pyrite to form chalcopyrite, bornite, and chalcocite ores. This study presents isotopic data that support bacterial sulfur reduction as the process that formed the essential precursor stage 1 pyrite, and the participation of basinal fluids in the hydrothermal second stage. A wide range of δ 34S values for early stage 1 pyrite (–11.1 to +28.0‰) supports the hypothesis that low-temperature, incomplete sulfate reduction from connate seawater sulfate and Fe-enriched oil-field brines took place in a compartmentalized petroleum reservoir by bacterial sulfate reduction. With the exception of a small proportion of Cu-Fe sulfides with δ 34S values between –2.0 and +2.0 per mil, the bulk of stage 2 Cu-Fe sulfides replaced earlier pyrite and mimic the broad range in δ 34Svalues (–12.7 and +19.0‰) of stage 1 pyrite. Sulfur from early pyrite was recycled with no significant homogenization, fractionation, or addition of new sulfur, and indicates the essential role of hydrocarbons and bacteria in the formation of the deposit. The δ 13C values of gangue calcite vary between –4.2 and –20.2 per mil and reflect a mixing of various proportions of oxidized, pyrobitumen-derived organic and inorganic carbon from the mineralizing fluid. Pyrobitumen in the ores has δ 13C values of –30 to –26 per mil, consistent with it being a residue of the original liquid petroleum. δ 18O values of K-feldspar in both ore and barren samples are similar (12.0–12.7‰) and are compatible with the fluids being of metamorphic, rather than magmatic, origin. The similar δ 18O ranges of calcite (2.7‰) and K-feldspar (0.7‰) suggest that they formed from the same hydrothermal fluid and that the fluid was in equilibrium with the host rocks. The 87Sr/86Sr ratios in calcite of 0.7041 to 0.7051 reflect isotopic ratios inherited from the subaerial andesitic rocks that overlay the deposit where the ore-forming fluids are thought to have originated.

Design of the Integrated Control Systems for Mineral Processing Plants

The paper presents modern tools for designing integrated plantwide control systems for mineral processes. The case concentrator is Pyhäsalmi, where Outokumpu Mintec has traditionally tested its new products and ideas in practice. The other concentrators discussed are Empresa Minera de Mantos Blancos (Chile) and Etibank Kure concentrator (Turkey), where Outokumpu Mintec has successfully made the latest installations of its automation systems and equipment. At the Mantos Blancos concentrators a novel particle size analyzer PSI-200 has led to significant progress in the control of grinding circuits. At the Kure concentrator the COURIER On-stream Analyzer has played an important role in enhancing the profitability of flotation. The Proscon 2100 automation system with its application software GRINDCON and FLOATCON has enabled the utilization of stabilizing expert control and the design of the integrated control system plantwide. At Kure concentrator an expert system using on-line information from ore type has been designed to be added to the integrated control system.

Edad y geoquimica isotopica Rb-Sr del yacimiento de cobre Mantos Blancos: relacion temporal con el magmatismo jurasico

ABSTRACT. Rb-Sr isotopic age and geochemistry of The Mantos Blancos copper deposit: temporal relation of the Jurassic magmatism. The Mantos Blancos volcanic sequence, host of the stratabound Cu (-Ag) deposit of the same name, has been studied for its Rb-Sr isotope geochemistry, to provide insights into the age and genesis of this important mineral deposit. Whole rock Rb-Sr ages of rock units characterized for their alteration pattern, allow the following generalizations: a- errorcrons from the NK unit (rocks with normal K2O contents and with little sodic alteration), yield ages of ca. 175 Ma, interpreted as the age of the host Mantos Blancos volcanic sequence; b- the ages of about 150 Ma obtained for the strongly altered ANa unit (sodic alteration), are interpreted to represent the age of hydrothermal alteration responsible for sodium metasomatism and its associated copper mineralization; c. intrusives emplaced into La Negra Formation and Mantos Blancos volcanic sequence may have been responsible for the thermal event causing the hydrothermal alteration process related to the ore mineralization. The initial 87Sr/86Sr of both NK and ANa units, and in calcite, which crystallized late in the paragenetic sequence of the ores, suggests that the hydrothermal fluids could not have been purely magmatic, nor of sea water origin, but could represent meteoric waters that have partially equilibrated with the host formations, or mixtures of different fluids.

Copper Extraction and Refining at Mantos Blancos

This paper describes a process especially developed to extract copper from copper chloride ores found at Mantos Blancos in Chile.