Enunciado y demostración del teorema de Poincaré Bendixson

Alteration assemblages developed at both the Bukit Botol and Bukit Ketaya sequences are significantly different between the two deposits. At the Bukit Botol deposit, the host felsic volcanic rocks are overprinted by two distinct hydrothermal alteration zones. An intense quartz-sericite-pyrite of the footwall represents a proximal zone and has Ishikawa (AI) indices higher than 95 and chlorite-carbonate-pyrite (CCPI) indices less than 60. A weak quartz- sericite assemblage occurs in the ore horizon rocks and represents a distal alteration zone. This zone has much lower AI (85-95) and CCPI less than 50. The hydrothermal zonations associated with the Bukit Botol deposit probably resemble the stratabound or semi- conformable quartz-sericite±chlorite-pyrite altered zone (e.g., Large, 1992) such as the Mount Chalmers deposit (Large and Both, 1980; Hunns, 2001) and the Brunswick No. 12 deposit, Canada (Yang et al., 2003).

Within the Bukit Botol deposit alteration zones, normal muscovite, phengite and paragonite were also identified on the SWIR profiles, and their assemblages can be clearly distinguished. In proximal alteration zones, the composition of muscovite shows a normal to phengitic muscovite, whereas the distal alteration zone is characterised by normal muscovite and paragonite. Molar element ratios of Na2O/Al2O3 versus K2O/Al2O3 and MgO/Al2O3 versus

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minerals controlled the intensity of alteration at the Bukit Botol deposit. The occurrence of phengite in the proximity of ore bodies has been described in several VHMS deposits such as Prince Lyell, Tasmania (Hendry, 1981) and Draa Sfar, Morocco (Belkabir et al., 2008). In addition, a distal paragonite zone surrounding the main sericite zone has also been described in the VHMS deposits of Aljustrel and Neves Corvo (Relvas et al., 1997).

Two types of alteration assemblages occur in the Bukit Ketaya deposit. The ore horizon rocks or distal alteration are characterised by quartz-chlorite-sericite-pyrite-pyrophyllite±kaolinite assemblages, whereas the weakly enveloped proximal alteration to the footwall is an intense quartz-chlorite-pyrite±carbonate±pyrophyllite assemblage. Both alteration zones are characterised by higher CCPI values more than 60 and variable AI values but slightly higher in the ore horizon than the footwall altered rocks. The Bukit Ketaya deposit also has a semi- conformable alteration type similar to that of the Bukit Botol deposit but probably demonstrates the chlorite altered zones described by Large (1992). Examples of the chlorite altered zones associated with VHMS deposits include the Woodlawn deposit, in Lachlan Fold Belt, NSW Australia and the Scuddle deposit, Western Australia (Large, 1992).

The SWIR spectra from both alterations show distinctive muscovite with minor pyrophyllite and paragonite but no chlorite spectral profile was identified. In addition, the XRD results also detect the presence of significance pyrophyllite, kaolinite and unidentified‘mica’. Chlorite was not identified in both alterations. However, molar element ratios of Na2O/Al2O3

versus K2O/Al2O3 and MgO/Al2O3 versus K2O/Al2O3 show that chlorite and muscovite are

the main alteration minerals reflecting the intensity of alteration at the Bukit Ketaya deposit, and the chlorite is mainly Mg-rich chlorite. Thus, it is evident that chlorite is present at both the alteration zone characteristics in the Bukit Ketaya deposit. However, the minor chlorite presence does not reflect on the XRD data identification; the mixed assemblages of muscovite

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and carbonate have absorption features at the same wavelength as the MgOH feature of chlorite, so the degree of Fe and Mg exchange cannot be easily determined by SWIR (Herrman et al., 2001, Jones et al., 2005). These distributions probably indicate a chlorite alteration pattern with a proximal Mg-chlorite and an intermediate to Fe-chlorite distal zone (McLeod and Stanton, 1984). This pattern has been observed in several VHMS deposits such as Thalanga (Paulick et al., 2001), Noranda (Riverin and Hodgson, 1980), Myra Falls (Jones et al., 2005) and at the Kuroko deposits, Japan (Urabe et al., 1983). In addition, the presence of pyrophyllite and kaolinite has also been reported from a few VHMS deposits such as the Western Tharsis deposit, Mount Lyell, Tasmania (Huston and Kamprad, 2001), the LaRonde Penna deposit, Abitibi, Quebec (Dube et al., 2007) and from several VHMS deposits in the Iberian Pyrite Belts (Relvas et al., 1997). According to Huston et al. (2011), the presence of advanced argillic alteration assemblages, clearly suggesting a significant magmatic- hydrothermal contribution.

5.7 Summary

1) The Bukit Botol and Bukit Ketaya deposits are characterised by distinctive mineralisation features forming stringer to massive sulphides at the footwall followed by barite and Fe+Mn±Si layers at the top that are comparable with those seen in many ancient felsic-hosted VHMS deposits. Preservation of these distinct ore zonations on the seafloor are capped by the formation of Fe+Mn±Si layers or ‘exhalites’.

2) The main sulphide phases common at both of the deposits are pyrite, chalcopyrite, sphalerite, rare galena and trace of Sn-bearing minerals. Ag-bearing and gold minerals are also present in the massive sulphide orbarite ores and have been found locally at the Bukit Botol deposit, but are absent at the Bukit Ketaya deposit. Late hydrothermal activity resulted in the formation of barite and Fe+Mn±Si layers.

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at both the deposits suggest that they were pure chemical sediments developed during formation of the massive sulphide deposit. The Fe+Mn±Si layers demonstrate a mixing of hydrothermal and hydrogenous origins. They were formed as a result of changing oxidation- reduction condition of fluid compositions with increasing distance from hydrothermal sources of the local submarine environments.

4) Different alteration assemblages were identified within the host volcanic rocks of the Bukit Botol and Bukit Ketaya deposits. These alteration zones form semi-conformable or stratabound-like alteration around both the deposits. The Bukit Botol deposit is characterised by proximal quartz-sericite-pyrite and distal quartz-sericite alteration zones, whereas distal quartz-chlorite-sericite-pyrite-pyrophyllite±kaolinite and proximal quartz-chlorite- pyrite±carbonate±pyrophyllite form the alteration assemblages of the Bukit Ketaya deposit. These data suggest that the different alteration assemblages may represent the deposits in one large hydrothermal system.