Ni-Co Laterite Deposits of the World—Database and Grade and Tonnage Models

Introduction

Nickel is an important metal in modern metallurgy with major uses in stainless steel (about 45 percent) and nickel-based alloys (about 39 percent). Since 1950, world Ni output continued to increase almost exponentially, reaching 1.43 Mt of mined nickel production in 2009. The London Metal Exchange Ni price at the end of 2010 was more than $11 per pound. Ni consumption in the United States was 152 Kt Ni in 2009. The United States has no active nickel mines or nickel reserves.

Ni-Co laterite deposits provide one of two major natural sources of nickel and cobalt. The economic importance of this deposit type expands in direct relation with industrialization of developing countries. Until now, the world nickel supply has been predominantly from sulfide deposits. According to Gleeson and others (2003), Dalvi and others (2004), and Mudd (2010), laterites contain about 70 percent of world nickel resources, have been mined for more than 100 years, and account for about 40 percent of world nickel production.

Included in this report is a database of 120 explored N-Co laterite deposits found worldwide (Appendix A). The database is a compilation of geologic and tonnage and grade data. Relevant data were collected from published and online Web sites and were found in recent issues of technical journals. The Ni-Co laterite deposits involved in our analysis are mostly well explored and are partially or entirely mined. These deposits contain reliable quantitative data on ore tonnages and Ni and Co grades.

The database, containing 66 fields, was compiled using File Maker Pro 8 software exported to Excel and tab-delineated spreadsheets. JMP 8 software was used for statistical tests and analyses. The compiled information on Ni-Co laterite deposits included the following topics: location, mineralogical subtypes, ore-processing methods related to the subtypes, development state, tonnage and grades, geological setting, morphological grouping, deposit age and distributions, and tonnage-grade models. Topic characteristics are presented and tested quantitatively. Statistical tests were performed to determine if delineated subtypes and groups of Ni-Co laterite deposits (such as mineralogical, shape, and age groups) are significantly different. Analysis of variance tests were made of differences in tonnage, mean nickel, and cobalt grades (logarithms). For this purpose, analysis of variance was used with means comparisons for each group using Student’s t-test.

Grade and tonnage models are important in mineral-resource assessments. One purpose of this report is to update a prior Ni laterite model by Singer (1986a, 1986b). New information about known deposits, as well as data on new deposits, published during the last decades are used in the models and summaries found in this paper. The compiled database (appendix A) contains data from 120 explored Ni laterite deposits, for which a subset of 117 deposits with more confident data was included in the grade-tonnage model. In the present updated grade-tonnage model, 46 more deposits were added than were found in the previous Ni laterite model prepared by Singer (1986a, 1986b). Ni-Co laterites develop by chemical weathering of ultramafic rocks and supergene enrichment of weathering products mostly under tropical climatic conditions. Resources of most deposits are mostly in place residuum, but a few are also redeposited lateritic material. Ni-Co laterites occur along the present or paleo surface above weathered bedrock. With respect to known classifications, three mineralogical subtypes of Ni-Co laterite deposits (Fe oxide, Mg hydrous silicate, and clay silicate) are selected by the dominant Ni-bearing mineral assemblage and statistically tested. The most economically important Ni laterite belt is confined to equatorial latitudes between 23.6 N to 23.0 S and includes almost all the youngest deposits and 72 percent of Cretaceous-Tertiary deposits.

Mineral-deposit models are important in exploration planning and quantitative resource assessments for two reasons: (1) grades and tonnages among deposit types vary significantly, and (2) deposits of different types are present in distinct geologic settings that can be identified from geologic maps. Mineral-deposit models combine the diverse geoscience information on geology, mineral occurrences, geophysics, and geochemistry used in resource assessments and mineral exploration. Globally based deposit models allow recognition of important features and demonstrate how common various features are. Well-designed deposit models allow geologists to deduce possible presence of mineral-deposit types in a given geologic environment, and the grade and tonnage models allow economists to estimate the possible economic viability of these resources. Thus, mineral-deposit models play a pivotal role in presenting geoscience information in a useful form to policy makers. The foundation of mineral-deposit models is information about known deposits.

The latest geologic data and newly developed grade and tonnage models for Ni-Co laterite deposits in digital form are presented. Included are computer files with information about deposits from around the world. Text files allow locations of all deposits to be plotted in geographic information system (GIS) programs. The data are presented in FileMaker Pro, as well as in text files, to make the information available to a broadly based audience. The deposits are positioned on a Google Earth image, where each deposit is supplied by concise information about geographical coordinates, tonnage, and grades, and a file is provided to show locations of deposits in Google Earth. The value of this information and any derived analyses depends critically on the consistent manner of data gathering. For this reason, we first discuss the rules used in this compilation. Next, the fields of the database are explained and analyzed. Finally, we provide new a new grade and tonnage model and analysis of the information in the file.

The main contributions of this project in the Ni laterite deposit model are the following:

• Widening deposit data on Ni laterites around the world, increasing the number of deposits by 65 percent in the database, and improving confidence in the tonnage-grade model.
• The notable change in the Ni laterite grade and tonnage model since the model by Singer (1986b) is that reporting Co has expanded from 20 percent to 56 percent of all deposits in the data set. This expansion allowed the addition of the 50th percentile for Co grades in the present model.
• Statistical investigations of mineralogical subtypes, age groups, and shape-size groups of deposits resulted in proper testing of quantitative characteristics to provide additional tools for resource assessments.

First posted May 26, 2011