Mark Bristow said he expected the Congo government would agree to amend the code, which was passed by the DRC Senate last month and would raise royalties on metals including gold, copper and cobalt.
Miners working in Congo include Randgold, Glencore, Ivanhoe and China Molybdenum Co.
Bristow said higher royalties would discourage investment but the key objection was that the new code dispensed with a clause in the previous charter protecting miners from changes to the code for 10 years.
Asked whether he considered the new code illegal, Bristow said: "It's attempting to disregard a law approved and passed by the House and the Senate. If the new code is attempting to ignore the previous laws then it is."
"We are engaging with everyone from the top to every ministry - prime minister to ministers of mines, ministries, civil society, senators, parliamentarians, foreign lenders, the whole nine yards," Bristow said.
"We haven't at this stage received any rejection. It's very early days. That's a step forward."
International miners operating in Congo were putting together a formal group to spearhead lobbying efforts, Bristow said. Chances of success are very high
"There's no one that's international and has significant investment in the mining industry (in Congo) that has declined the invitation (to join)," he said.
Randgold is asking for the code to be returned to the Mining Ministry for further consultation with miners. If this does not happen the company will mount a challenge through international arbitration, it said in a statement on Sunday.
"I believe the chances of success are very high, ultimately. The question is, does this have to get into a confrontation to get there?" Bristow said.
"What's being proposed results in a new investor on a new project ending up not making a single dollar return. That doesn't work and so ultimately that will drive a review."
"We've seen him (President Joseph Kabila) take stock of decisions in the past. Our strong recommendation is that this should happen with this legislation."
Randgold earlier on Monday doubled its annual dividend after profits rose by 14% in 2017.
Source: The African Report