The research work “Geology and Petrochemistry of Granitic Pegmatites in Jema’a Field” is a systematic study of the pegmatites in relation to the adjoining granitoids (biotite muscovite granite, albite granite and granite aplite) with a view to understanding their geological and geodynamic evolution and subsequent economic potential through the behavior of rare elements. The field work was conducted on a scale of 1:50, 000. 33 rocks and mineral separates extracted from pegmatites were analyzed. The samples were subdivided into two parts; one part was analyzed using X-Ray Fluorescence to generate data on major and minor elements, while Instrumental Neutron Activation Analysis was used to generate data on trace elements. The other part of the samples was made into thin section for petrographic studies. Petrochemical and petrographic interpretations concur on the changes in colour of micas from brown biotite in granitoids to blue muscovite, to purplish green mica to purple mica in the pegmatites corresponding to increase in rare elements (Rb, Cs, Na, Ta, Nb, Ga) and volatiles (P, H2O, F) from the granitoids into the pegmatites. This constitute a fractionation trend. This is also strongly supported by fairly consistent increase in Aluminum Saturation Index (A/CNK), normative corundum, normative albite, Lost on Ignition (LOI), differentiation Index (DI) and corresponding decrease in Ba, Zr and Ti. The pegmatites contains more fluxes and liquidus depressing elements (P, H2O, F) especially phosphorus. The granitoids (biotite muscovite granite, albite granite and granite aplite) are therefore fertile, peraluminous, siliceous and S-type and are parental to the pegmatites. The feldspars display perthitic textures which show incomplete solid solution and lowering of liquidus. The tectonic discrimination of the granitoids and the pegmatites show that they were formed within syncollisional, peraluminous, and active continental margin. The research suggest fractionation as a metallogenetic process. The genetic model presents the granitoids ; biotite muscovite granite, albite granite and granite aplite as products of internal chemical differentiation of a fractionating batholiths where NaO replaces K2O as the system is cooling. This is common to most granite-rare-elements-pegmatites systems all over the world. Fractionation via rare elements accumulations is therefore an exploration tool.
Table of Contents
1.0 INTRODUCTION
1.1 General Statement
1.2 Statement of the Problem
1.3 Aims and Objectives of the Present Work
1.4 Scope of the Present Work
2.0 LITERATURE REVIEW
2.1 Geologic Setting
3.0 MATERIALS AND METHODS
3.1 Materials Required
3.2 Exploration Method
3.2.1 Field Methods
3.2.1.1 Sampling
3.2.2 Laboratory Methods
3.2.2.1 Field Analysis
3.2.2.2 Sample Preparation
3.2.2.3 Sample Analysis
3.3 Conceptual Model Theories
3.3.1 Past
3.3.2 The Present
4.0 RESULTS
4.1 Petrographic Studies
4.1.1 Macro and Microscopic Studies
4.1.1.1Granitoids
4.1.1.2 Host Rocks
4.1.1.3 Feldspars
4.1.1.4 Mica
4.1.1.5 Tourmaline
4.2 Geochemistry
4.2.1 Major and Minor Elements Geochemistry
4.2.1.1 Interpretations of CIPW Norm
4.2.1.2 Thomton and Turtle, (1960) Differentiation Index
4.2.1.3 Interpretation of Niggli Norm
4.2.1.4 Classification of Granites after Chappell and White (1974)
4.2.1.5 Evidence from Magmatic Experiments
4.2.2 Petrochemistry of Rare Elements Granitoids and Pegmatites
4.2.2.1 Aluminum Saturation Index (A/CNK)
4.2.2.2 Variation (wt %) of CaO – NaO – K2O in Granitoids and Pegmatites
4.2.2.3 Classification of Granitoids using Q – A – P Diagram
4.2.2.4 Variation (ppm) of Rb – Ba – Sr for Differentiation of Granitoids
4.2.3 Trace Element Geochemistry
4.2.3.1 Trace Elements
4.3 Mineral Chemistry
4.3.1 Feldspars
4.3.2 Micas
4.3.3 Tourmaline
4.4 Tectonic Setting Discrimination of the Research Area
4.4.1 Fertile Granite in Aluminum Saturation Index Diagram coded by Tectonic affiliation and Geochemical signature
4.4.2 Tectonic Classification based on SiO2 Content and K2O/Na2O ratio
4.4.3 Rb (ppm) versus Nb + Y (ppm)
4.5 Lithological and Structural Relationships
CHAPTER FIVE
5.0 DISCUSSION OF RESULTS
5.1 Granitoids
5.2 Rare Elements as Exploration Tool
5.3 Feldspars
5.4 Muscovites
5.5 Tourmalines
5.6 Petrogenesis
5.6.1 Petrogenic Model
CHAPTER SIX
6.0 CONCLUSIONS AND RECOMMENDATION
6.1 Conclusions
6.2 Recommendations
Objectives and Research Themes
This thesis aims to conduct a systematic geological and geochemical study of the granitic pegmatites within the Jema’a pegmatite field in Kaduna State, Nigeria. The central research objective is to evaluate the geological evolution, geochemical characteristics, and economic potential of these pegmatites in relation to the surrounding granitoid bodies to better understand their mineralization, particularly regarding rare-element deposits.
- Geological and geodynamic evolution of granitic pegmatites.
- Mineralogical and geochemical characterization of granitoids and pegmatites.
- Evaluation of economic mineral potential with a focus on rare-element mineralization.
- Tectonic classification and petrogenetic modeling of the research area.
- Use of rare elements as exploration tools for identifying mineralized zones.
Excerpt from the Book
3.3.1 Past:
The first attempt to propose an origin for pegmatite was made by Brogger, (1890), suggesting that “Distinctive feature of pegmatite arises from the interplays of existing silicates melt and water vapour”. This view was held up to the end of 19th century. This model was letter ascribed to Jahns and Burnham, (1963). According to this model “Segregation of major alkalis can occur in significant degree when pegmatite magma becomes saturated with volatile constituents i.e. if both silicates melt and vapour is present in the system” (Jahns and Burnham, (1963)). In the 1970s and 80s, the most widely acceptable model of pegmatite genesis was that proposed by Jahns and Burnham, (1969) who proposed that “pegmatite formed by equilibrium crystallization of coexisting granitic melt and hydrous fluid at or slightly below the hydrous granite liquidus” (in Simmons, (2007)). This group held the view that pegmatite because of their pegmatitic texture crystallized slowly like normal granite.
Summary of Chapters
1.0 INTRODUCTION: This chapter introduces the Jema'a pegmatite field within the Nigerian pegmatite belt and outlines the scope, aims, and objectives of the research.
2.0 LITERATURE REVIEW: This section covers the regional geological setting of the Nigerian Basement complex and the tectonic framework of the Pan-African orogenic belt.
3.0 MATERIALS AND METHODS: This chapter details the field mapping, sampling, and analytical techniques (e.g., AAS, XRF, INAA) used to generate geochemical data.
4.0 RESULTS: This section presents the comprehensive petrographic and geochemical data obtained from granitoids, host rocks, and mineral separates.
5.0 DISCUSSION OF RESULTS: The chapter interprets the findings, providing insights into petrogenesis, tectonic settings, and the utility of rare elements as exploration tools.
6.0 CONCLUSIONS AND RECOMMENDATION: This final chapter synthesizes the study's conclusions regarding the pegmatite field and offers recommendations for future economic evaluation.
Keywords
Granitic Pegmatites, Jema'a Pegmatite Field, Petrochemistry, Geochemistry, Rare Elements, Fractionation, S-type Granites, Mineralization, Pan-African Orogeny, Aluminum Saturation Index, Feldspars, Muscovite, Tourmaline, Tectonics, Nigeria.
Frequently Asked Questions
What is the core focus of this research?
The research focuses on the geology and petrochemistry of granitic pegmatites in the Jema’a pegmatite field, Kaduna State, to determine their formation and mineralization potential.
Which pegmatite field is being studied?
The study is conducted in the Jema’a pegmatite field, which is the northwestern terminal point of the 400km Nigerian pegmatite belt.
What is the primary objective of the work?
The primary objective is to evaluate the economic significance of rare-element pegmatites by analyzing their mineralogical and geochemical relationships with associated granitoids.
What scientific methods were employed?
The methodology includes systematic 1:50,000 geological mapping, thin-section petrographic analysis, and geochemical analysis using Atomic Absorption Spectrometry, X-Ray Fluorescence, and Instrumental Neutron Activation Analysis.
What does the main body of the work cover?
The main body covers detailed petrochemical results, including major/trace element geochemistry, mineral chemistry of feldspars, micas, and tourmalines, and tectonic setting discrimination.
How is the research characterized by its keywords?
The research is characterized by terms such as Granitic Pegmatites, Geochemistry, Fractionation, S-type Granites, and Rare Elements, reflecting the focus on magmatic evolution and mineral exploration.
What is the significance of the "Albite subtype" classification mentioned?
The study concludes that the Jema'a pegmatites belong to the Albite subtype within the Lithium-Cesium-Tantalum (LCT) family, which is significant for understanding the melt's degree of fractionation.
How do the authors link pegmatites to the surrounding host rocks?
The authors demonstrate that the metasomatized host rocks (amphibolite/migmatite) indicate the migration of pegmatite-derived fluids, serving as a vital exploration tool for discovering mineralized zones.
- Quote paper
- Ahmed Isah Haruna (Author), 2012, Geology and Petrochemistry of Granitic Pegmatite in Jema’a Pegmatite Field, Kaduna State, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/200666
