|
Jacupiranga, Cajata |
|
|
São Paulo, Brazil |
| Main commodities:
P
|
|
 |
|
|
 |
Super Porphyry Cu and Au
|
IOCG Deposits - 70 papers
|
All papers now Open Access.
Available as Full Text for direct download or on request. |
|
|
The Jacupiranga apatite-carbonatite deposit is located near the town of Cajata, 200 km SW of São Paulo, and 35 km from the Atlantic coast, in southern Brazil, close to the border between the states of São Paulo and Paraná, #Location: 24° 42'S, 48° 08'W.
The Jacupiranga Igneous Complex (JIC) was intruded in the Early Cretaceous, approximately 130±4 Ma, contemporaneously with the widespread Paraná flood basalts. It intrudes a basement of the Coastal Domain, which is composed of variably metamorphosed Palaeoproterozoic supracrustal rocks now represented by mica-schists and gneisses. Approximately 20 km NW of the JIC, the major, ENE-WSW trending dextral Lancinha-Cubatao shear zone seperates the Coastal Domain from the Ribeira mobile belt which comprises a complex suite of low metamorphic grade meta-volcanosedimentary rocks of (peak metamorphic dates of 580 to 530 Ma), intruded by large calc-alkaline granite bodies. Other alkaline-ultramafic igneous complexes in the surrounding region, e.g., Juquiá, Itapirapuã and Mato Preto, occur as discordant intrusions in rocks of either or both basement tectonic units.
The JIC is a NNW-SSE elongated ellipsoidal intrusive body outcropping over an area of ~65 sq. km. It is largely composed of two ultramafic intrusions: dunites in the north, and clinopyroxenites (jacupirangite) in the south, with subordinate alkaline rocks and other lithologies. The carbonatites, which cover an area of ~0.7 sq. km, are the youngest intrusives and exclusively intrude the clinopyroxenite near the core of the complex, and occur as a series of pipe-like intrusions with sub-circular cross sections, and related dikes. Numerous rounded, large xenoliths of the clinopyroxenite (from a few cm up to about 5 m across) are found within the carbonatite, especially in the contact area between the more magnesium-rich intrusions, in the northern portion of the deposit, and in the southern, earlier intrusions. Drilling has demonstrated that the carbonatites extend to depths in excess of 440 m below surface, with a general dip angle of 80°. The main structures within the carbonatites include a NNW oriented fault zone, sets of joints and fractures. Magma flow structures, such as magmatic foliation are also recognised.
The JIC rocks are grouped into three categories: (i) ultramafic, comprising dunites, pyroxenites, carbonatites and lamprophyres; (ii) nepheline-bearing, comprising ijolites and syenites; and (iii) plagioclase-bearing, gabbros, diorites and monzonites. The carbonatites are sovites, rauhagites and beforsites and are composed of an assemblage that includes varying amounts of calcite, dolomite, apatite, magnetite, phlogopite, forsterite, pyrrhotite and pyrite, with lesser chalcopyrite, serpentine, pyrochlore, clinohumite and perovskite.
The carbonatite is complexly zoned, with areas that are sövitic with subordinate dolomite as small blebs and short stringers in the calcic mass, or in fine myemekite-like arrays in calcite, and includes intervals that are either phlogopite or olivine sövite. Other zones include calcitic-carbonatite with dense developments of dolomitic veins and dykes from cms to several metres thick, grading into broad zones of dolomitic carbonatite. The carbonatites are very variable in their carbonate type and content, which ranges from >90 to <30% CaO, with an average of 78% carbonates, with an overall calcite:dolomite ratio of 2.5:1, 12.5% apatite, 5 to 5.5% magnetite and <1.5% each of sulphides, mica and olivine. At least two main stages of carbonatite emplacement (and possibly as many as five) are indicated by the calcic and overprinting dolomitic zones, with apatite being enriched in the later dolomitic phase.
The carbonatite is cut by several joint systems, including radial and concentric patterns, as well as a large fault with associated brecciation and mylonitisation, all of which facilitated circulation of meteoric fluids during weathering. The rocks of the JIC are generally poorly exposed and covered by a thick mantle of lateritic soil, and have been subjected to deep weathering. The original carbonatite was exposed as peak that protruded 180 m above the local surface, which was covered by an irregular phosphate residuum of apatite, magnetite, clays and other insoluble accessories, totalling several million tonnes of 22% P2O5 and 26% Fe2O3
Fluorapatite is the only primary phosphate mineral, although two types, with ovoid and prismatic habits are evident. Mineralisation occurs as:
(i) veins or veinlets, usually strongly oriented, forming magmatic foliation;
(ii) small pods or patches, either associated with veins, or formed by individual clusters of short, acicular crystals;
(iii) disseminated, discrete grains (less common);
(i) massive aggregates of medium to coarse apatite grains, formed in the phoscorite (apatite+magnetite+olivine) rock, in the oldest carbonatite intrusion.
Magnetite is almost as abundant as apatite, with euhedral to subhedral crystals. Magnetite crystallisation was initiated early in the development of the carbonatite rock, coexisting with the bulk of liquidus phases. It continued to grow over an extensive period of time, although apatite growth was even more extensive, as demonstrated by earlier formed grains occurring as inclusions in magnetite, and many more (in particular apatite veins) that formed later than magnetite.
Reserves in 2006 (DNPM 2006 Mineral Annuary) - 85.1 Mt @ 5.45% P2O5, concentrated to grades of 36% P2O5.
Reserves in 1989 (Born, 1989) to a depth of ~340 m below the surface - 200 Mt @ ~5% P2O5.
This summary largely was based on Alves, 2008 (PhD thesis) and Born, 1989 (in Northolt et al., 1989)
The most recent source geological information used to prepare this decription was dated: 2008.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
|
|
|
Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
|
Top | Search Again | PGC Home | Terms & Conditions
|
|
