The application of forensic geology to investigate the substitution of zinc ingots between China and Brazil

Forensic geology in Brazil contributes to the public security, helps to preserve public order and safety. The Brazilian Federal Police employs 39 geologists who operate throughout the vast Brazilian territory. The Federal Police laboratories conduct geological and soil investigations and have benefited greatly from exchange of information with universities. This enables the sharing of data used for operational case work, the implementation of research and improvements in scientific methodologies, communication and collaborative work.

Zinc ingots were transported in containers aboard a vessel leaving a port in China on 2 February 2015. The cargo comprised 25 000 kg of zinc ingots estimated to be worth US$55 000. These were loaded at Xingang Harbour, in China, for export to Londrina, in Brazil, where they were to be used in the electrical industry.

Upon arrival in Brazil on 7 April 2015 the containers were found to contain 450 unmarked white woven plastic bags. The bags held a light brown sediment and weighed 11 610 kg. A chain of custody should have ensured that the zinc ingots arrived safely at their final destination in Brazil. It was subsequently suspected that the ingots were stolen and replaced with the sediment between ships at Busan Harbour, in South Korea, on 5 February 2015.

As the crime involved international theft, the Brazilian Federal Police was called to investigate and present a report to a Brazilian judge, who would decide whether the insurance company should reimburse the cargo owner. There was therefore a requirement for the Police and Federal University of Paraná (UFPR) to determine where the switch may have taken place. The journey of the containers containing the zinc ingots, from China to Brazil, is summarized in Table 1 and shown in Figure 1.

The external part of the container carrying the cargo showed evidence of tampering with the locking system, using physical force and leverage (Fig. 2). Forensic geologists from Brazilian Federal Police were contacted by the local police authority to assist with the investigation and to help identify the geographical provenance of the sediment.

In Londrina, the forensic experts initially conducted a visual examination of the container and the content of the bags, using a basic magnifying glass and a flashlight (Fig. 3a and b). It was verified that the bags contained a fine-grained and homogeneous material (Fig. 3c). These materials were randomly sampled from the bags, using a spade, and five plastic bags were filled with the material. In addition, a small piece of metal that was found on the wooden floor of the container was also submitted for analysis (Fig. 3d). All of the samples were sent to the Laboratory of Minerals and Rocks (LAMIR), at the Department of Geology, UFPR, in Curitiba, Brazil, for analysis and to identify the material type and possible source.

The analyses comprised conventional mineralogy, geochemistry and sedimentology. The objective of this analytical approach was to identify any evidence of geographic provenance that might indicate where the exchange of the zinc ingots occurred. As such, three representative samples of the sediment were taken from the container (C1, C2 and C3), one metallic fragment and one sample from each of the bags were collected for comparison purposes.

Mineralogical, chemical and particle size distribution studies were performed on the sediments and on samples of sand taken from the estuary at Paranaguá, close to the harbour, and from the coastline of Pontal, a neighboring city at the entrance of Paranaguá Bay. The mineralogy of the sediments was determined by X-ray diffraction (XRD) using a model PANalytical's EMPYREAN™ X-ray diffractometer fitted with the X'Celerator detector and a copper tube. Scans were run from 2θ angles of 3.5–70° at a scan rate of 10.16 s and a step size of 0.016°. The minerals were identified using the HighScore plus 3.0 software. The major elements were defined using X-ray fluorescence, using a model PANalytical Axios Max™ Spectrometer equipped with a 4 kV rhodium tube. The granulometry was performed using a laser diffraction granulometer, model CILAS 1064™, over the range from 0.004 to 500 µm.

Scanning electron microscopy (SEM) was used to provide information on the morphology and chemical composition of the metallic fragment found on the floor of the container. The SEM model was a Jeol-JSM-6010LA InTouchScope coupled with an energy dispersive x-ray analysis (EDAX) detector for elemental analysis, model EX-94410T1L11. In addition, the bags were also observed using this SEM to investigate the possibility for geological trace evidence.

The substituted sediments and sand from Paranaguá were also analysed for their light stable isotope values, including δ¹³C and δ¹⁸O. This was achieved through isotope ratio mass spectrometry analysis using a Thermo Scientific™ Delta V™ Advantage equipped with GasBench II housed at LAMIR. All of the samples were left to react with 100% H₃PO₄ in a hot block at 70°C for 2 h. The results were reported in per mil units (δ[‰] = [(R_sample − R_standard)/R_standard] × 1000), where R is the isotopic ratio of ¹³C/¹²C or ¹⁸O/¹⁶O, normalized to the VPBD scale using NBS19, IAEA-C01, IAEA-C08 and IAEA-C09 standards. The standard deviation for the standards during the analytical section was smaller than ±0.04‰ for both δ¹³C and δ¹⁸O.

The particle size distribution for the substituted sediment found in the container bags is presented in Figure 4. It consisted mostly of medium silt, with an average particle diameter of 0.022 mm, while the samples collected from a beach along the Paranaguá coastline were classified as a fine to medium sand, averaging from 0.179 to 0.271 mm.

The geochemical studies provided an understanding of the composition of the material from both the container bags and the Paranaguá beach sand (Fig. 5c and Table 2). The results showed two distinct groups of samples. The sediments found inside the container (C1, C2 and C3) revealed lower amounts of SiO₂, similar contents of TiO₂ and MnO and higher concentrations of Al₂O₃, CaO, Fe₂O₃, MgO, K₂O, Na₂O, SO₃, P₂O₅, and SrO. On the other hand, the beach sand samples indicated a composition mostly of SiO₂ (95.7–98.3%).

The mineralogical studies showed that the sediment in the containers (C1, C2 and C3) was composed predominantly of quartz, calcite, dolomite, plagioclase, alkali-feldspar, mica (probably) and a layer of silicate mineral with dominant reflection identified at 14 Angstroms. It is important to note XRD is semi-quantitative and the relative concentrations are therefore not absolute. In comparison, the beach sand collected in Paranaguá Harbour region was basically composed of quartz (Table 2).

Since the container was transferred between ships at Busan Harbour, in South Korea, the investigators suspected that this could possibly have provided the opportunity for the substitution of the zinc ingots. It was also necessary to check whether the replacement had occurred at Paranaguá Harbor when the container was transferred to a truck. For this reason, a comparison of the regional geology of Paranaguá Harbour and Busan Harbour was undertaken (Figs 6a & 6b). According to Choi et al. (2011), the coastal sediments from South Korea harbours are composed mainly of alumino-silicate minerals and quartz derived from the erosion of the adjacent land mass and calcium carbonates derived from marine plants and animals (Fig. 6b). In comparison, the beach sand from Paranaguá Harbour in Brazil consists predominantly of quartz (see Fig. 5).

The results of SEM and EDAX investigations of the metal fragment found on the floor of the container confirmed that it was high-purity zinc metal (Fig. 7d). It was interpreted as possibly a broken fragment of one of the stolen ingots.

Stable isotope studies were performed to evaluate the geographical provenance of the material. Samples from Paranaguá Harbour, Busan Harbour and the sediments found in the container were analysed for the carbon and oxygen inorganic stable isotopes. The results of the analysis show that only the samples from container sediments (C1, C2 and C3) showed isotopic signatures, which is in accordance with their composition, as provided as a carbonate minerals (from XRD; Table 3). These results are also in agreement with Woo & Khim (2006), which classified different carbonate materials in the Busan Harbour region (Table 3). Using the isotopic data, it was possible to compare the δ¹⁸O with the global distribution of the oxygen-18 ratio on the seawater surface (Schmidt et al. 1999), considering the rock/fluid equilibrium. This shows that the material is consistent with a location in the Northern Hemisphere, including Busan and Xingang harbours and surrounding areas and, most importantly, excluding Paranaguá Harbour region.

SEM images from a fragment of one of the sample bags (Fig. 8a) showed the presence of microscopic traces of a cnidarian (Fig. 8b, c & d). The Cnidaria phylum comprises predominantly the Anthozoa class, which includes marine invertebrates like corals that, when living in colony, may build coral reefs (Won et al. 2001). When observing the distribution of coral reefs around the world, it is possible to note that a high number of coral species live between the Pacific and Indian Oceans (Veron 2000), and a significant amount adjacent to South Korea and China. On the contrary, the region close to the Paranaguá Harbour shows no coral reefs. Indo-Pacific reefs have a greater diversity when compared with Brazil (Paulay 1997). However, the Brazilian coast does not contain such quantities and their distribution is restricted mainly to the northeastern part of Brazil.

Collaboration between the Brazilian Federal Police and universities provided the opportunity to develop a forensic approach to investigate substituted zinc ingots samples being transported by ship from China to Brazil.

By combining the results from different analytical techniques, including sedimentological studies (particle size distribution), mineralogy (XRD, SEM, EDAX and carbon and oxygen isotopes) and micropalaeontology (Cnidarian microtraces), it was possible to demonstrate that the substituted material was most likely to have originated from Asia and not South America, therefore excluding the Paranaguá region as the source. Moreover, the isotopic signals were compatible with other investigations showing these to align with South Korea. Since the containers of zinc ingots were transferred from one ship to another in the South Korea region, in Busan Harbour, this is the most likely place for the cargo exchange to have occurred.

The authors thank the Brazilian Federal Police Department in Paraná for the permission to use the information related to the case, the UFPR for the integrated studies and the LAMIR for conducting the analyses on the samples. We also thank the reviewers (Drs Duncan Pirrie, Roger Dixon, Laurance Donnelly and Rob Fitzpatrick) for assistance.

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

FADSS: Conceptualization (Lead), Data curation (Lead), Formal analysis (Lead), Funding acquisition (Lead), Investigation (Lead), Methodology (Lead), Project administration (Lead), Resources (Lead), Software (Lead), Supervision (Lead), Validation (Lead), Visualization (Lead), Writing – Original Draft (Lead), Writing – Review & Editing (Lead); MPNES: Conceptualization (Supporting), Data curation (Supporting), Formal analysis (Equal), Funding acquisition (Supporting), Investigation (Supporting), Methodology (Supporting), Project administration (Supporting), Resources (Supporting), Software (Supporting), Supervision (Supporting), Validation (Supporting), Visualization (Supporting), Writing – Original Draft (Supporting), Writing – Review & Editing (Supporting); AMBR: Conceptualization (Equal), Data curation (Supporting), Formal analysis (Supporting), Funding acquisition (Lead), Investigation (Equal), Methodology (Lead), Project administration (Supporting), Resources (Lead), Software (Lead), Supervision (Lead), Validation (Lead), Visualization (Supporting), Writing – Original Draft (Supporting), Writing – Review & Editing (Supporting); RDOM: Conceptualization (Supporting), Data curation (Supporting), Formal analysis (Supporting), Funding acquisition (Supporting), Investigation (Supporting), Methodology (Supporting), Project administration (Supporting), Resources (Supporting), Software (Supporting), Supervision (Supporting), Validation (Supporting) Writing – Original Draft (Supporting), Writing – Review & Editing (Supporting).