Petrogenetic significance of LA-ICP-MS trace-element data on quartz from the Borborema Pegmatite Province, northeast Brazil

Abstract

Quartz from different zones within five granitic pegmatites of the rare-element class from the Borborema Pegmatite Province in northeast Brazil were analysed for fourteen trace elements using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The concentrations of Li (6À150 ppm), B (1À9 ppm) and Ge (1À23 ppm) in quartz show a positive correlation with Al (30À770 ppm). The concentrations of these elements increase from the border zone to the quartz core of pegmatites of the spodumene or lepidolite subtypes. The Ge concentrations in the quartz core are the highest so far reported in igneous quartz. In the less evolved pegmatites of the beryl-columbite subtype, the Al, Li, B, and Ge concentrations in quartz from all zones remain at the same level as the border and wall zones. The Ti concentrations in quartz from the core of the more evolved pegmatites are below 3 ppm (with Al >250 ppm), contrasting with 7À25 ppm (with Al <280 ppm) in samples from the border and wall zones of the less evolved and more evolved pegmatites. The concentrations of Al, Li, B, Ge, and Ti in quartz are therefore confirmed as good indicators of the degree of magma fractionation and analyses of pegmatite quartz cores can be used for exploration purposes to distinguish pegmatites with high metallogenic potential. Atoms of Li and Al are incorporated into quartz such that Li/Al ranges between 0.75 and 1.0. This suggests a coupled substitution of the form Si 4+ $ (Li + + Al 3+ ). The other elements analysed either showed an erratic distribution (e.g. Be and P) or were below the respective limits of detection (Na, K, Rb, Ca, Sr, Mn, Fe) in most samples.

Estudo da suscetibilidade ao escurecimento por radiação gama de quartzo róseo-leitoso da província pegmatítica da Borborema

“…As impurezas dominantes são Al e Li e, em menor concentração, Ti e Ge. Tais elementos são comumente encontrados na estrutura do quartzo natural, na forma de impurezas substitucionais ou intersticiais (Götze et al 2004, Larsen et al 2004, Beurlen et al 2009b. Não foi detectada a presença de P, Mg, Ca e Sr. A grande concentração de Cr, Fe e Ni medida apenas na variedade rósea pode ser explicada pela presença de inclusões sólidas microscópicas, de morfologia arredondada, observadas no resíduo da digestão ácida.…”

Trace Elements of Pegmatitic Quartz and Their Regional Distribution in two Pegmatite Fields of Southern Norway

“…Systematic gradients of quartz trace elements from the contact to the core of pegmatites which are described, for example, for the Borborema pegmatites, Brazil [16], were not detected [5].…”

Quartz sand resources in the Santa Maria Eterna formation, Bahia, Brazil: A geochemical and morphological study

“…Table 2 compiles the main impurities of commercial powders. Full references of high quality raw material can be found in Santos et al (2014), Suzuki et al (2012), Beurlen et al (2011), andIwasaki et al (1991) for Brazilian quartz; Müller et al (2012Müller et al ( , 2007Müller et al ( , 2003 for Norwegian quartz; and G€ otze (2009) and G€ otze et al (2004) for quartz from different countries. The comparison of quartz from Santa Maria Eterna to other sources of high purity quartz described in literature, shows that the studied sand has a very low Al content as it is found in nature.…”