Geological Setting and Mineralization of Iron Ore, Rare Earth Elements, and Associated Metals in Kithiori Area of Marimanti, Tharaka Nithi County, Kenya.

Abstract

The study area is located in Marimanti area in Tharaka Nithi County, Kenya, and it is bound by the following coordinates: 00° 10’ 50” S – 00° 09’ 10” S and 37° 58’ 20” E – 37° 40’ 00” E. The area is also located within the Neo-Proterozoic Mozambique Mobile Belt. The research was conducted with the main aim of understanding the structural, mineralogical, and geological setting of the iron ore deposits, rare earth elements, and associated metals in the Kithiori area. The study was also conducted to investigate the relationship between the iron ore deposits, REE, associated metals, and the host rock units trying to ascertain the nature and modes of occurrence in relation to alteration processes and the effects of structural developments. X-Ray Diffraction, X-Ray Fluorescence, and Petrographical analysis were used. Sample preparation for the three methods was conducted at the Ministry of Petroleum and Mining - Kenya, and the analysis of the latter was done at the University of Nairobi petrological laboratory at the Department of Geology. The findings of this study indicate that iron ore is centrally confined and is associated with pyroxenite rocks. The study reports polymetallic ores such as pyrophanite (Mn0.5 Ni0.5 O3 Ti.), magnesioferrite (Fe2 Mg O4), cuprospinel (Cu0.86 Fe2.14 O4), ilmenite (Fe1.1 O3 Ti0.9), magnetite (Fe3 O4), and Franklinite (Al0.028 Fe1.91 Mg0.035 Mn0.426 O4 Zn0.602) among others, occurring in varying quantities. It should also be noted that rare mineral species have been identified in considerable quantities. These rare minerals include osbornite (N4 Ti4 - 16.8%) which is mostly considered extraterrestrial with very few known natural terrestrial occurrences the world over. Other rare minerals include moissanite – 28% and brunogeierite 16.6% among others all of which are in excess of 15% of the analyzed samples. From the structural perspective, it is noted that pyroxene pegmatites play an important role in the mineralization of iron ore through various hypotheses that have been presented in the report. Geologically, the area is dominated by gabbro, anorthosite, and dolerite containing plagioclase feldspars ranging from 70% to 93%. These rocks appear to have intruded into the host rock. The study has categorized the anorthosites into two main suites based on their physical properties, Type 1 Kithiori Anorthositic Suite, and Type 2 Kithiori Anothorsitic Suite. The study has outlined various hypothetical modes of formation for the gabbroic rocks. A unique combination of anorthite and albite in one sample has been identified, reported, and recorded in the report. The report further indicates that multifaceted magmatism processes such as vii fractionation, elemental incompatibility, and filter pressing played a crucial role in the geology of the area. Elemental studies have also been carried out. The findings show that a decrease in Ca, Si, Al, and Na is accompanied by an increase in Fe and Ti from the gabbroic rocks to the ores. It is important to note the presence of Rare Earth Elements (REEs) such as Nd, Ce, Gd, Dy, Ho, Tm, La, Yb, Sc, and Y among others. Platinum Group Elements (PGEs) such as Pt, Pd, and Rh have been reported. Various theories for the occurrence of these elements have been enumerated in this study report some of which allude to the discordant properties of the constituent elements in the respective rock units. With great interest, the presence of hydrothermal activity indicator minerals in various samples is noted. These minerals (and their respective percentages in the samples) include Sellaite (30%), Klockmannite (10%), Permingeatite (1.2% and 1.0%), Sphene (8.3% and 1.9%), Hawleyite (4.9%) among others. These minerals together with some of the associated structures suggest a strong presence of hydrothermal action having taken place in the study area. This phenomenon has been likened to various other areas of similar geology and mineralization for ease of comparison and inference in regards to the occurrence of iron ore and other associated elements and metals in the area. Bearing the scope of the study, several recommendations have been fronted with the aim of getting the complete narrative of the mineralogical and structural transformation, the economic viability of the iron ore, REE, and other metals.