Peaks very similar to that are very common for Au NPs. For example: http://drajput.com/research/gold_nanoparticles_preparation.php and https://www.researchgate.net/publication/230588414_Thermal_diffusivity_measurement_of_spherical_gold_nanofluids_of_different_sizesconcentrations (Figure 3). It probably means the average size of your NPs is roughly around 40-50 nm. The smaller the NPs (as long as they are bigger than about 5 nm), the peak in the visible region will be at lower wavelength and less broad - of course, less broad, more intense peak also usually means less broad size distribution, better monodispersity of NPs, but definite conclusions about monodispersity and even average size usually can't be made just from UV/Vis, one reason being that UV/Vis spectra are also influenced by the ligand and the solvent.

Article Thermal diffusivity measurement of spherical gold nanofluids...

Yes.The 530nm peak is due to Surface Plasmon Resonanace.300 nm peak is due to inter band absorption.300nm peak is not by SPR. It is explained as electron hole pair.With 530nm peak we can calculate the size of the particle.

You may find the following results of us are useful to you.

"Linear optical absorption and photoluminescence emission

properties of gold nanoparticles prepared by laser ablation

technique", Appl Phys A (2012) 108:81–89; DOI 10.1007/s00339-012-7016-1;

Wish you good luck and happy new year 2016.

link.springer.com/content/pdf/10.1007%2Fs00339-012-7016-1.pdf