HIBRIDNI ALGORITAM OPTIMIZACIJE ROJA ČESTICA I OPTIMIZACIJE SIVOGA VUKA ZA JEDNODIMENZIONALNO INVERZNO MODELIRANJE AUDIOFREKVENCIJSKE MAGNETOTELURIKE S KONTROLIRANIM IZVOROM (CSAMT)

The Controlled Source Audio-frequency Magnetotellurics (CSAMT) is a geophysical method utilizing artificial electromagnetic signal source to estimate subsurface resistivity structures. One-dimensional (1D) inversion modelling of CSAMT data is non-linear and the solution can be estimated by using global optimization algorithms. Particle Swarm Optimization (PSO) and Grey Wolf Optimizer (GWO) are well-known population-based algorithms having relatively simple mathematical formulation and implementation. Hybridization of PSO and GWO algorithms (called hybrid PSO-GWO) can improve the convergence capability to the global solution. This study applied the hybrid PSO-GWO algorithm for 1D CSAMT inversion modelling. Tests were conducted with synthetic CSAMT data associated with 3-layer, 4-layer and 5-layer earth models to determine the performance of the algorithm. The results show that the hybrid PSO-GWO algorithm has a good performance in obtaining the minimum misfit compared to the original PSO and GWO algorithms. The hybrid PSO-GWO algorithm was also applied to invert CSAMT field data for gold mineralization exploration in the Cibaliung area, Banten Province, Indonesia. The algorithm was able to reconstruct the resistivity model very well which is confirmed by the results from inversion of the data using standard 2D MT inversion software. The model also agrees well with the geological information of the study area.Audiofrekvencijska magnetotelurika s kontroliranim izvorom (CSAMT) geofizička je metoda koja se koristi izvorom umjetnoga elektromagnetskog signala za procjenu struktura otpornosti ispod površine. Jednodimenzionalno (1D) inverzno modeliranje CSAMT podataka nelinearno je te se rješenje može procijeniti korištenjem algoritama za globalnu optimizaciju. Algoritam roja čestica (PSO) i algoritam sivoga vuka (GWO) dobro su poznati algoritmi koji se temelje na populaciji i imaju relativno jednostavnu matematičku formulaciju i implementaciju. Hibridizacija PSO i GWO algoritama (hibridni PSO-GWO) može poboljšati sposobnost konvergencije prema globalnom rješenju. U ovom istraživanju primijenjen je hibridni PSO-GWO algoritam za 1D CSAMT inverzno modeliranje. Provedeno je testiranje sa sintetičkim CSAMT podatcima povezanim s 3-slojnim, 4-slojnim i 5-slojnim modelima zemlje kako bi se odredile performanse algoritma. Rezultati su pokazali kako hibridni PSO-GWO algoritam ima dobre performanse u postizanju minimalne neusklađenosti u usporedbi s originalnim PSO i GWO algoritmima. Hibridni PSO-GWO algoritam također je primijenjen za inverziju CSAMT terenskih podataka s ciljem istraživanja mineralizacije zlata u području Cibaliung, provincija Banten, Indonezija. Algoritam je uspio vrlo dobro rekonstruirati model otpornosti, što potvrđuju rezultati inverznoga modeliranja korištenjem standardnoga softvera za inverziju 2D magnetotelurskih podataka. Rezultati modela također se dobro podudaraju s geološkim informacijama istraživanoga područja

Identification of gold mineralization zones of low sulfidation epithermal systems using geoelectrical and magnetic methods in Ciparay area, Cibaliung

Abstrak. Cibaliung merupakan daerah pertambangan mineral yang berada di Provinsi Banten. Hal ini, dibuktikan dengan adanya lubang tambang emas di daerah Cikoneng dan Cibitung. Penelitian tentang geofisika penting dilakukan guna menemukan cadangan emas baru di daerah Ciparay yang terletak di Sebelah Tenggara Cikoneng dan Cibitung. Metode geofisika yang digunakan di antaranya magnetik, resistivitas, dan induced polarization (IP). Metode magnetik digunakan sebagai survei pendahuluan untuk menggambarkan keberadaan struktur geologi pengontrol mineralisasi emas. Melalui peta reduce to pole dapat diketahui adanya tanda-tanda keberadaan struktur geologi yang ditunjukkan oleh anomali negatif (-220 hingga -135 nT) di Bagian Barat Daya daerah penelitian. Hasil teknik edge detectors menunjukkan adanya pola struktur dengan arah Northwest (NW) dan North-Northeast (NNE) yang dominan berada di Bagian Barat Daya sebelah Utara daerah penelitian. Metode resistivitas dan IP digunakan sebagai survei detail untuk menentukan keberadaan mineral yang terkandung dalam batuan. Hasilnya menunjukkan bahwa zona potensi mineralisasi ditunjukkan oleh anomali tinggi (resistivitas 50 ohm.m dan chargeability 40 msec). Resistivitas tinggi diduga sebagai respons batuan induk andesitic sedangkan, nilai chargeability tinggi merupakan respons dari hadirnya mineral-mineral bijih seperti emas dan perak. Zona potensi mineralisasi berada pada posisi patok 350-800 dengan arah persebaran mengikuti arah struktur geologi pengontrolnya yaitu NW dan NNE. Abstract. Cibaliung is a mineral mining area located in Banten Province. The area including gold mining in Cikoneng and Cibitung areas. Geophysical research is important to find new gold reserves at the Ciparay area, located in the Southeast of Cikoneng and Cibitung. Geophysical methods used include magnetic, resistivity, and IP. The magnetic method was applied as a preliminary survey to delineate the presence of the geological structure controlling the gold mineralization. Based on the RTP map, signs of the presence of geological structures are shown by anomalies -220 to -135 nT in the Southwestern part of the study area. The results of edge detector techniques show the existence of structural patterns in the direction of NW and NNE which are dominant in the Southwestern North of the study area. The resistivity and IP methods are employed for detailed investigation in order to obtain to determine the presence of minerals contained in rocks. The results show that the mineralized zones are indicated by high resistivity ( 50 ohm.m) and high chargeability ( 40 msec). High resistivity response is caused by andesitic source rock whereas, high chargeability response is related to the presence of ore minerals such as gold and silver. The mineralization prospect zone is indicated at the position of 350-800 and its direction corresponds to the direction of its geological structure namely NW and NNE.Keywords: New gold reserves, Negative magnetic anomalies, High resistivity, High chargeability.

HYBRID PARTICLE SWARM OPTIMIZATION AND GREY WOLF OPTIMIZER ALGORITHM FOR CONTROLLED SOURCE AUDIO-FREQUENCY MAGNETOTELLURICS (CSAMT) ONE-DIMENSIONAL INVERSION MODELLING

The Controlled Source Audio-frequency Magnetotellurics (CSAMT) is a geophysical method utilizing artificial electromagnetic signal source to estimate subsurface resistivity structures. One-dimensional (1D) inversion modelling of CSAMT data is non-linear and the solution can be estimated by using global optimization algorithms. Particle Swarm Optimization (PSO) and Grey Wolf Optimizer (GWO) are well-known population-based algorithms having relatively simple mathematical formulation and implementation. Hybridization of PSO and GWO algorithms (called hybrid PSO-GWO) can improve the convergence capability to the global solution. This study applied the hybrid PSO-GWO algorithm for 1D CSAMT inversion modelling. Tests were conducted with synthetic CSAMT data associated with 3-layer, 4-layer and 5-layer earth models to determine the performance of the algorithm. The results show that the hybrid PSO-GWO algorithm has a good performance in obtaining the minimum misfit compared to the original PSO and GWO algorithms. The hybrid PSO-GWO algorithm was also applied to invert CSAMT field data for gold mineralization exploration in the Cibaliung area, Banten Province, Indonesia. The algorithm was able to reconstruct the resistivity model very well which is confirmed by the results from inversion of the data using standard 2D MT inversion software. The model also agrees well with the geological information of the study area