# Compositional Analysis of Chalcopyrite Using Calibration-Free Laser-Induced Breakdown Spectroscopy
## 4 Discussion  
Chalcopyrite is one of the economically important minerals, not only because of its copper content, but also due to presence of other precious elements as impurities such as Au, Ag, Se, and Ti [41; 42]. In XRF analysis, Si was detected with a weight percentage of 5.7%, while Se and Ag were identified as minor elements with concentrations of about 0.7% and 0.1% by weight. However, these elements could not be spotted in the LIBS spectrum. Similarly, Ca was detected with LIBS and quantified as 0.9% by  
Figure 6: Elemental composition of Chalcopyrite sample measured with CF-LIBS and XRF techniques.  
weight, whereas it could not be measured by XRF. This difference in results obtained by these two techniques can be attributed to variation in concentration of different elements at various points of the sample surface. To reduce this inhomogeneity, the sample was grinded and pressed into pellet form, but it was still very hard to remove it completely. In addition, in case of minor elements such as Se and Ag, it is possible that concentrations of these elements in the chalcopyrite sample will be lower than the limit of detection of the LIBS setup used in this experiment. However, the CF-LIBS technique proved to be effective in measuring the concentration of major elements, Cu and Fe, with reasonably good accuracy. To improve the sensitivity of LIBS, different techniques such as microwave-assisted LIBS, magnetic field-assisted LIBS, and the use of double pulse, resonant laser, spark discharge, and long pulse lasers can be employed. Utilizing these techniques can help in making CF-LIBS a suitable tool for elemental analysis of geological materials of unknown elemental composition in significantly low concentrations.  
Copper concentrations of about 58% by weight, as confirmed by both CF-LIBS and XRF analysis, reveals that the chalcopyrite sample analyzed is a high-grade Cu bearing mineral, which is desirable in the mineral industry. The presence of Ag and Se in trace amounts enhances further the economic value of chalcopyrite found in the area of Neelum valley. LIBS has the ability to show excellent quantitative results using calibration methods, provided the availability of matrix-matched reference materials. Mostly, in case of geological samples, reference materials are not available, and this fact hinders the use of the calibration method for quantification of geological sample of unknown composition [43]. In this scenario, the CF-LIBS method appears to be a suitable and effective alternative to the calibration method. In some previous studies, the CF-LIBS method was utilized for measurement of elemental composition of geological samples such as limestone, granite, malachite, and nephrite, and results were compared with standard techniques such as energy dispersive X-ray spectroscopy (EDX), X-ray fluorescence (XRF), and laser ablation-time of flight-mass spectrometer (LA-TOF-MS) [24; 25; 26; 44; 45]. In all of these studies, quantitative results obtained with CF-LIBS showed reasonable agreement with the standard analytical techniques. Hence, it can be concluded that without the availability of a suitable reference material, CF-LIBS analysis of multi-elemental minerals can still give very good quantitative results, and the method can be used for real applications in mineral extraction and exploration.