Assessment of kimberlite diamond grade by the indicator minerals chemical composition in Lunda region of Angola

<p>To determine a diamond grade (ct/t) in the Lunda district kimberlites using the chemical composition of the KIM (indicator minerals) frequency of occurrence of their cluster groups (CG) we performed statistical analysis of the chemical composition of pyropes (3478 grains) of Cr-diopsides (714) and picroilmenites (1582) of the 6 kimberlite diamond deposits. Classification procedures of cluster and correlation – factor analysis were used (Ivanov, 2017). Significant correlation coefficients were determined between the variations of KIM compositions and diamond content in kimberlites. Figure 2 shows the distribution of diamond contents in 6 kimberlite pipes, correlated with the distribution of pyropes G10 (Dawson et al., 1975), chromium diopsides CG S6, as well as CG of picroilmenites – 12b and P12-16 in their frequency of occurrence, the interpretation of which is reduced to the following conclusions. The proportions of pyropes CG G10 in kimberlites of 5 pipes control the linear growth (R<sup>2</sup>=0.97) of the diamond content in pipes to the center of the Saurimo structure, excluding the CAT-E42 pipe. With a relatively high diamond grade, the proportion of  G10 in this pipe is low, which may be related to the extremely low quality of its diamonds. In kimberlites. This indicator is typical for the Catoca and Luele pipes, with the maximum proportions of low-ferrous picroilmenites (11.0% and 13.9%). In the NE direction, the conditions for the preservation of diamonds in kimberlites decrease, which affects their low diamond grade (0.2-0.4 ct / t), which decreases exponentially (R<sup>2</sup>=0.98) with an increase in the TiO<sub>2</sub> content in picroilmenites. The proportion of CG S6 Cr-diopsides belonging to the high-pressure variety of the deep mantle lithosphere (coesite facies) (Sobolev, 1971) increases in the kimberlites of the central part of the Saurimo structure to 15-32% and controls the high diamond content of the Catoca, CAT-E42 and Luele pipes (Fig. 1). The established regularities of changes in the frequency of occurrence of CG KIMs in the NE-SW direction in the Lunda kimberlite region confirm the regional pyrope trend of N. V. Sobolev's diamond content and other KIMs correlations with the diamond content of kimberlites in this region. They also meet the "rule of V. A. Milashev" on reducing the diamond content of kimberlites to the periphery of regional structural units of kimberlite provinces (Zinchenko et al., 2016).</p><p>Sobolev N.V. Mineralogical criteria of diamond-bearing kimberlites. Geology and geophysics. No. 3. 1971, 70-80.</p><p>Dawson J.B., Stephens W.E. Statistical classification of garnets from kimberlites and xenoliths.J. Geol. 1975. 83, 589-60</p><p>Gurney D. D., Moore R. O. Geochemical correlation between kimberlite minerals and diamonds of the Kalahari Craton. 1994.,12–24.</p><p>Ivanov A. S. Statistical analysis of indicator minerals of kimberlites. Proceedings of the XIII All-Russian Fersman Session. KSC RAS.  Apatity. 2017,  172 -181.</p><p>Zinchenko, V., Felix J. T., Francisco J. Diamondiferous trend of the kimberlites in the Lunda region (Angola)//35th International Geological Congress Abstracts. Cape Town. South Africa. 2016.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.0e3eea868d0066419941161/sdaolpUECMynit/12UGE&app=m&a=0&c=7ecb3e7dd388e9edb98f52df0a9411a0&ct=x&pn=gnp.elif&d=1" alt="" width="581" height="346"></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.960b89858d0069888941161/sdaolpUECMynit/12UGE&app=m&a=0&c=cdf3e97fdd49a7a10a2127127c90c0ff&ct=x&pn=gnp.elif&d=1" alt="" width="590" height="127"></p><p> </p>

IACS: past, present, and future of the International Association of Cryospheric Sciences

The International Association of Cryospheric Sciences (IACS) became the eighth and most recent association of IUGG at the general assembly in Perugia, Italy, in July 2007. IACS was launched in recognition of the importance of the cryosphere within the Earth system, particularly at a time of significant global change. It was the first new association of the union to be formed in over 80 years and IACS celebrated its 10th anniversary only a year before the IUGG centennial. The forbearers of IACS, however, stretch back even further than IUGG, starting with the formation of the Commission Internationale des Glaciers (CIG) by the International Geological Congress in 1894. Here we record the history of the transition from CIG to IACS, the scientific objectives that drove activities and changes, and some of the key events and individuals involved.

Apa itu Antroposen?

Artikel ini menjelaskan tentang apa yang dimaksud dengan Antroposen. Secara definisi, Antroposen dapat dipahami sebagai epos baru setelah Holosen yang ditandai oleh banyaknya tanda-tanda aktivitas manusia yang dapat dideteksi secara stratigrafis. Dalam sejarah manusia memang selalu mempengaruhi Bumi. Namun, kumpulan aktivitas-aktivitas manusia telah mempengaruhi Bumi secara masif hingga mengubah sistem fundamental Bumi itu sendiri. Itulah mengapa Paul Crutzen mengusulkan bahwa Bumi tidak lagi berada pada epos Holosen. Di antara banyak geolog terjadi perdebatan mengenai permulaan Antroposen. Ada tiga hipotesis utama: revolusi agrikultur, revolusi industri, dan pasca Perang Dunia II. Sampai saat ini, banyak geolog yang menyetujui bahwa Antroposen dapat dideteksi secara signifikan secara stratigrafis pada periode pasca Perang Dunia II. Bukti-buktinya meliputi banyaknya limbah anthropogenic , melimpahnya technofossil , dan jejak-jejak geokemis yang bisa diukur melalui observasi strata inti es atau sedimen danau di Greenland atau Antartika. Bukti lain bisa diambil lewat efek bom nuklir. Sampai saat ini Antroposen belum diformalisasikan dalam skala waktu geologis, tetapi mayoritas ilmuwan yang ikut serta dalam International Geological Congress 2016 sepakat bahwa Antroposen dapat diformalisasi. Konsekuensi dari beralihnya Holosen ke Antroposen tidak dapat diketahui secara pasti, sebab perubahan yang terjadi bersifat dinamis dan berjalan dalam suatu trajektori yang belum bisa diketahui. Namun, satu hal yang pasti adalah bahwa efek dari aktivitas-aktivitas manusia saat ini akan ada selama berjuta tahun.

35th Session of the InternationalGeological Congress (Cape Town, 2016)

The results of the 35th Session of the International Geological Congress held in 2016 in Cape Town (South Africa) are discussed in this paper. The major scientific problems discussed at the most popular sections are considered. Among them are the early stages in the evolution of the Earth, studies of mineral resources worldwide, the problems of the deep Earth structure, as well as modern fields of mineralogy.