Abstract
The Intex laterite deposit in Mindoro, Philippines is derived from the weathering of the ultramafic rocks under a tropical climate. This study investigates the several types of serpentines and the effect of the degree of chemical weathering of ultramafic rocks and laterites on the enrichment of Ni in the deposit. The five types of serpentines are differentiated based on their textural features and Raman spectral data. Type I, type II, type III, and type IV serpentines contain a low amount of NiO (average 0.15 wt%), and their formation is linked to the previous exhumation of the ultramafic body. Conversely, type V serpentines show the highest NiO contents (average 1.42 wt%) and have the composition of serpentine-like garnierites, indicating a supergene origin. In the limonite horizon, goethite is the main ore mineral and shows high NiO contents of up to 1.68 wt%, whereas the Mn-oxyhydroxides (i.e., asbolane and lithiophorite–asbolane intermediate) display substantial amounts of CoO (up to 11.3 wt%) and NiO (up to 15.6 wt%). The Ultramafic Index of Alteration (UMIA) and Index of Lateritization (IOL) are used to characterize the different stages of weathering of rocks and laterites. The calculated index values correspond to a less advanced stage of weathering of the Intex laterites compared with the Berong laterites. The Berong deposit is a Ni-Co laterite deposit in the Philippines, which is formed from the weathering of the serpentinized peridotite. The less extreme degree of weathering of the Intex laterites indicates less advanced leaching, and thereby the re-distribution of Ni, Si, and Mg from the limonite towards the saprolite horizon may have resulted in the poor precipitation of talc-like (kerolite-pimelite) and sepiolite-like (sepiolite-falcondoite) phases in the studied saprolite horizon. Nickel in the Intex deposit has undergone supergene enrichment similar to other humid tropical laterite deposits.
Highlights
Nickel laterite deposits are formed from chemical weathering of ultramafic rocks and contain a significant amount of Ni, and to some extent, Co and Sc [1,2,3,4]
A typical Ni laterite profile consists from the bottom to top: (i) the unaltered or serpentinized ultramafic rocks, (ii) the saprolite horizon, and (iii) the limonite horizon
This study investigates the different types of serpentine found in the bedrock and the saprolite horizon
Summary
Nickel laterite deposits are formed from chemical weathering of ultramafic rocks and contain a significant amount of Ni, and to some extent, Co and Sc [1,2,3,4]. Nickel laterite deposits are commonly divided into three types based on the main Ni hosting minerals such as oxide deposits, hydrous Mg silicates, and clay silicate deposits [6,7,8]. Each of these categories has implications on the assessment of resource and mineral processing [1,9]. (ii) the saprolite horizon, and (iii) the limonite horizon This profile is often covered by goethite-rich ferricrete [10]
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